Editing Thai language (section)

==== Early Old Thai ====
{{further|Proto-Tai}}
Early Old Thai also apparently had velar fricatives {{IPA|/x ɣ/}} as distinct phonemes. These were represented by the now-obsolete letters ฃ ''kho khuat'' and ฅ ''kho khon'', respectively. During the Old Thai period, these sounds merged into the corresponding stops {{IPA|/kʰ ɡ/}}, and as a result the use of these letters became unstable.

At some point in the history of Thai, an alveolo-palatal nasal phoneme {{IPA|/ɲ/}} also existed, inherited from [[Proto-Tai]]. A letter ญ ''yo ying'' also exists, which is used to represent an alveolo-palatal nasal in words borrowed from [[Sanskrit]] and [[Pali]], and is currently pronounced {{IPA|/j/}} at the beginning of a syllable but {{IPA|/n/}} at the end of a syllable.  Most native Thai words that are reconstructed as beginning with {{IPA|/ɲ/}} are also pronounced {{IPA|/j/}} in modern Thai, but generally spelled with ย ''yo yak'', which consistently represents {{IPA|/j/}}. This suggests that {{IPA|/ɲ/}} > {{IPA|/j/}} in native words occurred in the pre-literary period. It is unclear whether Sanskrit and Pali words beginning with {{IPA|/ɲ/}} were borrowed directly with a {{IPA|/j/}}, or whether a {{IPA|/ɲ/}} was re-introduced, followed by a second change {{IPA|/ɲ/}} > {{IPA|/j/}}. The [[northeastern Thai]] dialect [[Isan language|Isan]] and the [[Lao language]] still preserve the phoneme /ɲ/, which is represented in the [[Lao script]] by  ຍ, such as in the word  ຍຸງ ({{IPA|/ɲúŋ/}}, ''mosquito''). This letter is distinct from the phoneme {{IPA|/j/}} and its Lao letter ຢ, such as in the word  ຢາ ({{IPA|/jàː/}}, ''medicine''). The distinction in writing has been lost in the informal writing of the Isan language with the Thai script and both sounds are represented by ย {{IPA|/j/}} (See: [[Comparison of Lao and Isan]]).

Proto-Tai also had a glottalized palatal sound, reconstructed as {{IPA|/ʔj/}} in Li Fang-Kuei (1977{{Full citation needed|date=November 2012}}). Corresponding Thai words are generally spelled หย, which implies an Old Thai pronunciation of {{IPA|/hj/}} (or {{IPA|/j̊/}}), but a few such words are spelled อย, which implies a pronunciation of {{IPA|/ʔj/}} and suggests that the glottalization may have persisted through to the early literary period.