Pronunciation 2), the diphthong reading, is traditionally regarded as the correct one. However, the monophthong reading 1) has been recorded as early as Han Dynasty, and Sui-Tang rhyme books record both. Both readings are reflected in Sino-xenic readings in non-Sinitic languages, although the diphthong readings dominate in compounds. Axel Schüssler postulates that all pronunciations can eventually be traced back to liquid initials, i.e. 1,2) **laːts, 3) **hlaːts.
The three pronunciations are cognate. Within Chinese, they are cognate with 太 (OC *tʰaːds, “too, excessively”), 泰 (OC *tʰaːds, “big”). Wang (1982) also lists 誕 (OC *l'aːnʔ, “big, magniloquent, ridiculous”) as a cognate, which Schuessler (2007) suggests is cognate with 延 (OC *lan, *lans, “to extend”) instead. There are no unambiguous Tibeto-Burman cognates. Proto-Tibeto-Burman *taj (“big”), from which came Written Tibetan མཐེ་བོ (mthe bo, “thumb”), Anong tʰɛ (“big; large; great”), Mikir tʰè, ketʰè ("id."), Burmese တယ် (tai, “very”), is often compared with. There is no final –s in the Tibeto-Burman words, but a –y, which, according to James Matisoff, "indicates emergent quality in stative verbs". Also compare Chinese 多 (OC *ʔl'aːl, “many, much”), 都 (OC *taː, “all”).
This is often the first half two-character shorthand name of universities, for example 東大 (Tōdai, “Tokyo University”). Reading of first character often changes from kun'yomi to on'yomi.