In phonetics and phonology, gemination (), or consonant lengthening (from Latin geminatio 'doubling', itself from gemini 'twins'), is an articulation of a consonant for a longer period of time than that of a singleton consonant. It is distinct from stress. Gemination is represented in many writing systems by a doubled letter and is often perceived as a doubling of the consonant. Some phonological theories use "doubling" as a synonym for gemination, others describe two distinct phenomena.
Consonant length is a distinctive feature in certain languages, such as Arabic, Berber, Danish, Estonian, Hindi, Hungarian, Italian, Japanese, Kannada, Polish and Turkish. Other languages, such as English, do not have phonemic consonant geminates.
Consonant gemination and vowel length are independent in languages like Arabic, Japanese, Finnish and Estonian; however, in languages like Italian, Norwegian and Swedish, vowel length and consonant length are interdependent. For example, in Norwegian and Swedish, a geminated consonant is always preceded by a short vowel, while an ungeminated consonant is preceded by a long vowel. A clear example are the Norwegian words tak ('ceiling or roof' of a building, pronounced with a long /ɑː/), and takk ('thanks', pronounced with a short /ɑ/).
Lengthened fricatives, nasals, laterals, approximants and trills are simply prolonged. In lengthened stops, the obstruction of the airway is prolonged, which delays release, and the "hold" is lengthened.
Gemination of consonants is distinctive in some languages and then is subject to various phonological constraints that depend on the language.
In some languages, like Italian, Swedish, Faroese, Icelandic, and Luganda, consonant length and vowel length depend on each other. A short vowel within a stressed syllable almost always precedes a long consonant or a consonant cluster, and a long vowel must be followed by a short consonant. In Classical Arabic, a long vowel was lengthened even more before permanently-geminate consonants.
In other languages, such as Finnish, consonant length and vowel length are independent of each other. In Finnish, both are phonemic; taka /taka/ 'back', takka /takːa/ 'fireplace' and taakka /taːkːa/ 'burden' are different, unrelated words. Finnish consonant length is also affected by consonant gradation. Another important phenomenon is sandhi, which produces long consonants at word boundaries when there is an archiphonemic glottal stop |otaʔ se| > otas se 'take it!'
In addition, in some Finnish compound words, if the initial word ends in an e, the initial consonant of the following word is geminated: jätesäkki 'trash bag' [jætesːækːi], tervetuloa 'welcome' [terʋetːuloa]. In certain cases, a v after a u is geminated by most people: ruuvi 'screw' /ruːʋːi/, vauva 'baby' [ʋauʋːa]. In the Tampere dialect, if a word receives gemination of v after u, the u is often deleted (ruuvi [ruʋːi], vauva [ʋaʋːa]), and lauantai 'Saturday', for example, receives a medial v [lauʋantai], which can in turn lead to deletion of u ( [laʋːantai]).
Distinctive consonant length is usually restricted to certain consonants. There are very few languages that have initial consonant length; among them are Pattani Malay, Chuukese, Moroccan Arabic, a few Romance languages such as Sicilian and Neapolitan as well as many High Alemannic German dialects, such as that of Thurgovia. Some African languages, such as Setswana and Luganda, also have initial consonant length: it is very common in Luganda and indicates certain grammatical features. In colloquial Finnish and in Italian, long consonants occur in specific instances as sandhi phenomena.
The difference between singleton and geminate consonants varies within and across languages. Sonorants show more distinct geminate-to-singleton ratios while sibilants have less distinct ratios. The bilabial and alveolar geminates are generally longer than velar ones.
The reverse of gemination reduces a long consonant to a short one, which is called degemination. It is a pattern in Baltic-Finnic consonant gradation that the strong grade (often the nominative) form of the word is degeminated into a weak grade (often all the other cases) form of the word: taakka > taakan (burden, of the burden). As a historical restructuring at the phonemic level, word-internal long consonants degeminated in Western Romance languages: e.g. Spanish /ˈboka/ 'mouth' vs. Italian /ˈbokka/, both of which evolved from Latin /ˈbukka/. 
Written Arabic indicates gemination with a diacritic (ḥaraka) shaped like a lowercase Greek omega or a rounded Latin w, called the شَدَّة shadda: ّ . Written above the consonant that is to be doubled, the shadda is often used to disambiguate words that differ only in the doubling of a consonant where the word intended is not clear from the context. For example, in Arabic, Form I verbs and Form II verbs differ only in the doubling of the middle consonant of the triliteral root in the latter form, e. g., درس darasa (with full diacritics: دَرَسَ) is a Form I verb meaning to study, whereas درّس darrasa (with full diacritics: دَرَّسَ) is the corresponding Form II verb, with the middle r consonant doubled, meaning to teach.
In Berber, each consonant has a geminate counterpart, and gemination is lexically contrastive. The distinction between single and geminate consonants is attested in medial position as well as in absolute initial and final positions.
In addition to lexical geminates, Berber also has phonologically-derived and morphologically-derived geminates . Phonologically-derived geminates can surface by concatenation (e.g. [fas sin] 'give him two!') or by complete assimilation (e.g. /rad = k i-sli/ [rakk isli] 'he will touch you'). The morphological alternations include imperfective gemination, with some Berber verbs forming their imperfective stem by geminating one consonant in their perfective stem (e.g. [ftu] 'go! PF', [fttu] 'go! IMPF'), as well as quantity alternations between singular and plural forms (e.g. [afus] 'hand', [ifassn] 'hands').
Word-initial gemination occurs in various Malay dialects, particularly those found on the east coast of the Malay Peninsula such as Kelantan-Pattani Malay and Terengganu Malay. Gemination in these dialects of Malay occurs for various purposes such as:
In most instances, the absence of this doubling does not affect the meaning, though it may confuse the listener momentarily. The following minimal pairs represent examples where the doubling does affect the meaning in most accents:
In some dialects gemination is also found for some words when the suffix -ly follows a root ending in -l or -ll, as in:
In some varieties of Welsh English, the process takes place indiscriminately between vowels, e.g. in money [ˈmɜn.niː] but it also applies with graphemic duplication (thus, orthographically dictated), e.g. butter [ˈbɜt̚.tə]
In Ancient Greek, consonant length was distinctive, e.g., μέλω [mélɔː] 'I am of interest' vs. μέλλω [mélːɔː] 'I am going to'. The distinction has been lost in the standard and most other varieties, with the exception of Cypriot (where it might carry over from Ancient Greek or arise from a number of synchronic and diachronic assimilatory processes, or even spontaneously), some varieties of the southeastern Aegean, and Italy.
Gemination is common in both Hindi and Urdu. It does not occur after long vowels and is found in words of both Indic and Arabic origin, but not in those of Persian origin. In Urdu, gemination is represented by the Shadda diacritic, which is usually omitted from writings, and mainly written to clear ambiguity. In Hindi, gemination is represented by doubling the geminated consonant, enjoined with the Virama diacritic.
Germination of aspirated consonants in Hindi are formed by combining the corresponding non-aspirated consonant followed by its aspirated counterpart. In vocalised Urdu, the shadda is placed on the unaspirated consonant followed by the short vowel diacritic, followed by the do-cashmī hē, which aspirates the preceding consonant. There are few examples where an aspirated consonant is truly doubled.
In Standard Italian, word-internal geminates are usually written with two consonants, and geminates are distinctive. For example, bevve, meaning 'he/she drank', is phonemically /ˈbevve/ and pronounced [ˈbevve], while beve ('he/she drinks/is drinking') is /ˈbeve/, pronounced [ˈbeːve]. Tonic syllables are bimoraic and are therefore composed of either a long vowel in an open syllable (as in beve) or a short vowel in a closed syllable (as in bevve). In varieties with post-vocalic weakening of some consonants (e.g. /raˈdʒone/ → [raˈʒoːne] 'reason'), geminates are not affected (/ˈmaddʒo/ → [ˈmaddʒo] 'May').
Double or long consonants occur not only within words but also at word boundaries, and they are then pronounced but not necessarily written: chi + sa = chissà ('who knows') [kisˈsa] and vado a casa ('I am going home') [ˈvaːdo a kˈkaːsa] (the latter example refers to central and southern standard Italian). All consonants except /z/ can be geminated. This word-initial gemination is triggered either lexically by the item preceding the lengthening consonant (e.g. by preposition a 'to, at' in [a kˈkaːsa] a casa 'homeward' but not by definite article la in [la ˈkaːsa] la casa 'the house'), or by any word-final stressed vowel ([parˈlɔ ffranˈtʃeːze] parlò francese 's/he spoke French' but [ˈparlo franˈtʃeːze] parlo francese 'I speak French').
In Latin, consonant length was distinctive, as in anus 'old woman' vs. annus 'year'. Vowel length was also distinctive in Latin, but was not reflected in the orthography. Geminates inherited from Latin still exist in Italian, in which [ˈanno] anno and [ˈaːno] ano contrast with regard to /nn/ and /n/ as in Latin. It has been almost completely lost in French and completely in Romanian. In West Iberian languages, former Latin geminate consonants often evolved to new phonemes, including some instances of nasal vowels in Portuguese and Old Galician as well as most cases of /ɲ/ and /ʎ/ in Spanish, but phonetic length of both consonants and vowels is no longer distinctive.
In Norwegian, gemination is indicated in writing by double consonants. Gemination often differentiates between unrelated words. As in Italian, Norwegian uses short vowels before doubled consonants and long vowels before single consonants. There are qualitative differences between short and long vowels:
In Polish, consonant length is indicated with two identical letters. Examples:
Consonant length is distinctive and sometimes is necessary to distinguish words:
Double consonants are common on morpheme borders where the initial or final sound of the suffix is the same as the final or initial sound of the stem (depending on the position of the suffix). Examples:
Punjabi is written in two scripts, namely, Gurmukhi and Shahmukhi. Both scripts indicate gemination through the uses of diacritics. In Gurmukhi the diacritic is called the áddak which is written before the geminated consonant and is mandatory. In contrast, the shadda, which is used to represent gemination in the Shahmukhi script, is not necessarily written, retaining the tradition of the original Arabic script and Persian language, where diacritics are usually omitted from writing, except to clear ambiguity, and is written above the geminated consonant. In the cases of aspirated consonants in the Shahmukhi script, the shadda remains on the consonant, not on the do-cashmī he.
Gemination is specially characteristic of Punjabi compared to other Indo-Aryan languages like Hindi-Urdu, where instead of the presence of consonant lengthening, the preceding vowel tends to be lengthened. Consonant length is distinctive in Punjabi, for example:
In Russian, consonant length (indicated with two letters, as in ванна [ˈvannə] 'bathtub') may occur in several situations.
Minimal pairs (or chronemes) exist, such as подержать [pədʲɪrˈʐatʲ] 'to hold' vs поддержать [pədʲːɪrˈʐatʲ] 'to support', and their conjugations, or длина [dlʲɪˈna] 'length' vs длинна [dlʲɪˈnːa] 'long' adj. f.
In Spanish there are geminated consonants in Caribbean Spanish when /l/ and /ɾ/ in syllabic coda are assimilated to the following consonant. Examples of Cuban Spanish:
Luganda is unusual in that gemination can occur word-initially, as well as word-medially. For example, kkapa /kːapa/ 'cat', /ɟːaɟːa/ jjajja 'grandfather' and /ɲːabo/ nnyabo 'madam' all begin with geminate consonants.
There are three consonants that cannot be geminated: /j/, /w/ and /l/. Whenever morphological rules would geminate these consonants, /j/ and /w/ are prefixed with /ɡ/, and /l/ changes to /d/. For example:
In Japanese, consonant length is distinctive (as is vowel length). Gemination in the syllabary is represented with the sokuon, a small tsu: っ for hiragana in native words and ッ for katakana in foreign words. For example, 来た (きた, kita) means 'came; arrived', while 切った (きった, kitta) means 'cut; sliced'. With the influx of gairaigo ('foreign words') into Modern Japanese, voiced consonants have become able to geminate as well: バグ (bagu) means '(computer) bug', and バッグ (baggu) means 'bag'. Distinction between voiceless gemination and voiced gemination is visible in pairs of words such as キット (kitto, meaning 'kit') and キッド (kiddo, meaning 'kid'). In addition, in some variants of colloquial Modern Japanese, gemination may be applied to some adjectives and adverbs (regardless of voicing) in order to add emphasis: すごい (sugoi, 'amazing') contrasts with すっごい (suggoi, 'really amazing'); 思い切り (おもいきり, omoikiri, 'with all one's strength') contrasts with 思いっ切り (おもいっきり, omoikkiri, 'really with all one's strength').
In Turkish gemination is indicated by two identical letters as in most languages that have phonemic gemination.
Loanwords originally ending with a phonemic geminated consonant are always written and pronounced without the ending gemination as in Arabic.
Gemination also occurs when a suffix starting with a consonant comes after a word that ends with the same consonant.
Estonian has three phonemic lengths; however, the third length is a suprasegmental feature, which is as much tonal patterning as a length distinction. It is traceable to allophony caused by now-deleted suffixes, for example half-long linna < *linnan 'of the city' vs. overlong linna < *linnahan 'to the city'.[clarification needed]
Consonant length is phonemic in Finnish, for example takka [ˈtɑkːɑ] ('fireplace', transcribed with the length sign [ː] or with a doubled letter [ˈtɑkkɑ]) and taka [ˈtɑkɑ] ('back'). Consonant gemination occurs with simple consonants (hakaa : hakkaa) and between syllables in the pattern (consonant)-vowel-sonorant-stop-stop-vowel (palkka) but not generally in codas or with longer syllables. (This occurs in Sami languages and in the Finnish name Jouhkki, which is of Sami origin.) Sandhi often produces geminates.
Both consonant and vowel gemination are phonemic, and both occur independently, e.g. Mali, maali, malli, maallinen (Karelian surname, 'paint', 'model', and 'secular').
In many Finnish dialects there are also the following types of special gemination in connection with long vowels: the southwestern special gemination (lounaismurteiden erikoisgeminaatio), with lengthening of stops + shortening of long vowel, of the type leipää < leippä; the common gemination (yleisgeminaatio), with lengthening of all consonants in short, stressed syllables, of the type putoaa > puttoo and its extension (which is strongest in the northwestern Savonian dialects); the eastern dialectal special gemination (itämurteiden erikoisgeminaatio), which is the same as the common gemination but also applies to unstressed syllables and certain clusters, of the types lehmiä > lehmmii and maksetaan > maksettaan.
In Wagiman, an indigenous Australian language, consonant length in stops is the primary phonetic feature that differentiates fortis and lenis stops. Wagiman does not have phonetic voice. Word-initial and word-final stops never contrast for length.
In written language, consonant length is often indicated by writing a consonant twice (ss, kk, pp, and so forth), but can also be indicated with a special symbol, such as the shadda in Arabic, the dagesh in Classical Hebrew, or the sokuon in Japanese.
In the International Phonetic Alphabet, long consonants are normally written using the triangular colon ː, e.g. penne [penːe] ('feathers', 'pens', also a kind of pasta), though doubled letters are also used (especially for underlying phonemic forms, or in tone languages to facilitate diacritic marking).
Doubled orthographic consonants do not always indicate a long phonetic consonant.