Rhotacism ()[1] or rhotacization is a sound change that converts one consonant (usually a voiced alveolar consonant: /z/, /d/, /l/, or /n/) to a rhotic consonant in a certain environment. The most common may be of /z/ to /r/.[2] When a dialect or member of a language family resists the change and keeps a /z/ sound, this is sometimes known as zetacism.

The southern, Tosk dialects, the base of Standard Albanian, changed /n/ to /r/, but the northern, Gheg dialects did not:[2]

Aquitanian *l changed to the tapped r between vowels in Basque.[3] It can be observed in words borrowed from Latin; for example, Latin caelum (meaning "sky, heaven") became zeru in Basque (caelum > celu > zeru; compare cielo in Spanish). The original l is preserved in the Souletin dialect: caelum > celu > zelü.

Western dialects of Finnish are characterised by the pronunciation /r/ or /ɾ/ of the consonant written d in Standard Finnish kahden kesken- kahren kesken (two together = one on one).[example needed] The reconstructed older pronunciation is .

In Manx, Scottish Gaelic and some dialects of Irish, a /kn/ cluster developed into /kr/, often with nasalization of the following vowel, as in Scottish Gaelic cnoc [krɔ̃xk] ‘hill’.[2]

All surviving Germanic languages, which are members of the North and West Germanic families, changed /z/ to /r/, implying a more approximant-like rhotic consonant in Proto-Germanic.[4] Some languages later changed all forms to r, but Gothic, an extinct East Germanic language, did not undergo rhotacism.

Note that the Modern German forms have levelled the rhotic consonant to forms that did not originally have it. However, the original sound can still be seen in some nouns such as Wesen, "being" (from the same root as war/waren) and Verlust, "loss" (from the same root as verlieren/verloren).

Because of the presence of words that did not undergo rhotacisation from the same root as those that did, the result of the process remains visible in a few modern English word pairs:

Intervocalic /t/ and /d/ are commonly lenited to [ɾ] in most accents of North American and Australian English and some accents of Irish English and English English,[6] a process known as tapping or less accurately as flapping:[7] got a lot of /gɒtə lɒtə/ becomes [gɒɾə lɒɾə]. Contrast is usually maintained with /r/, and the [ɾ] sound is rarely perceived as /r/.[2]

In Central German dialects, especially Rhine Franconian and Hessian, /d/ is frequently realised as [ɾ] in intervocalic position. The change also occurs in Mecklenburg dialects. Compare Borrem (Central Hessian) and Boden (Standard German).

Reflecting a highly-regular change in pre-Classical Latin, intervocalic /s/ in Old Latin, which is assumed to have been pronounced [z], invariably became r, resulting in pairs such as these:

Intervocalic s in Classical Latin suggests either borrowing (rosa) or reduction of an earlier ss after a long vowel or a diphthong (pausa < paussa, vīsum < *vīssum < *weid-tom). The s was preserved initially (septum) and finally and in consonant clusters.

Old Latin honos became honor in Late Latin by analogy with the rhotacised forms in other cases such as genitive, dative and accusative honoris, honori, honorem.[9]

Another form of rhotacism in Latin was dissimilation of d to r before another d and dissimilation of l to r before another l, resulting in pairs such as these:

In many words in which the ancients said s, they later said r... foedesum foederum, plusima plurima, meliosem meliorem, asenam arenam

In Neapolitan, rhotacism affects words that etymologically contained intervocalic or initial /d/.

In Galician-Portuguese, rhotacism occurred from /l/ to /r/, mainly in consonant clusters ending in /l/ such as in the words obrigado, "thank you" (originally from "obliged [in honourably serving my Sir]"); praia, "beach"; prato, "plate" or "dish"; branco, "white"; prazer/pracer, "pleasure"; praça/praza, "square". Compare Spanish obligado (obliged), playa, plato, blanco, placer, plaza from Latin obligatus, plagia, platus, blancus (Germanic origin), placere (verb), platea.

In contemporary Brazilian Portuguese, rhotacism of /l/ in the syllable coda is characteristic of the Caipira dialect. Further rhotacism in the nationwide vernacular includes planta, "plant", as [ˈpɾɐ̃tɐ], lava, "lava", as /ˈlarvɐ/ (then homophonous with larva, worm/maggot), lagarto, "lizard", as [laʁˈɡaʁtu] (in dialects with guttural coda r instead of a tap) and advogado, "lawyer", as [ɐ̞de̞vo̞ʁˈɡadu]. The nonstandard patterns are largely marginalised, and rhotacism is regarded as a sign of speech-language pathology or illiteracy.

Rhotacism, in Romanesco, shifts l to r before a consonant, like certain Andalusian dialects of Spanish. Thus, Latin altus (tall) is alto in Italian but becomes arto in Romanesco. Rhotacism used to happen when l was preceded by a consonant, as in the word ingrese (English), but modern speech has lost that characteristic.

Another change related to r was the shortening of the geminated rr, which is not rhotacism. Italian errore, guerra and marrone "error", "war", "brown" become erore, guera and marone.

Thus, Latin caelum ‘sky; heaven’ became Romanian cer, Latin fenestra ‘window’ Romanian fereastră and Latin felicitas ‘happiness’ Romanian fericire.

Some northern Romanian dialects and Istro-Romanian also changed all intervocalic [n] to [ɾ] in words of Latin origin.[10] For example, Latin bonus became Istro-Romanian bur: compare to standard Daco-Romanian bun.

Rhotacism (mola > mora, filum > fir, sal > sare) exists in Gallo-Italic languages as well in Lombard, Western Lombard, Alpine Lombard and Ligurian.

In Umbrian but not Oscan, rhotacism of intervocalic s occurred as in Latin.[11]

Rhotacism is particularly widespread in the island of Sicily, but it is almost completely absent in the Sicilian varieties of the mainland (Calabrese and Salentino). It affects intervocalic and initial /d/: cura from Latin caudam, peri from Latin pedem, 'reci from Latin decem.

In Andalusian Spanish, particularly in Seville, at the end of a syllable before another consonant, l is replaced with r: Huerva for Huelva. The reverse occurs in Caribbean Spanish: Puelto Rico for Puerto Rico (lambdacism).

In Sanskrit, words ending in -s (-สฺ) other than -as ([เสียงอะ] + สฺ) become -r (-รฺ) in sandhi with a voiced consonant:

That is not properly rhotacism since r and s are then simply allophones.

In some South Slavic languages, rhotacism occasionally changes a voiced palatal fricative [ʒ] to a dental or alveolar tap or trill [r] between vowels:

The beginning of the change is attested in the Freising manuscripts from the 10th century AD, which show both the archaism (ise 'which' < *jь-že) and the innovation (tere 'also' < *te-že). The shift is also found in individual lexical items in Bulgarian dialects, дорде 'until' (< *do-že-dĕ) and Macedonian, сеѓере (archaic: 'always'). However, the results of the sound change have largely been reversed by lexical replacement in dialects in Serbia and Bosnia from the 14th century.

Dialects in Croatia and Slovenia have preserved more of the lexical items with the change and have even extended grammatical markers in -r from many sources that formally merged with the rhotic forms that arose from the sound change: Slovene dialect nocor 'tonight' (< *not'ь-sь-ǫ- + -r-) on the model of večer 'evening' (< *večerъ). The reversal of the change is evident in dialects in Serbia in which the -r- formant is systematically removed: Serbian veče 'evening'.