Origins

Early evidence of kho khuat can be found in the Ram Khamhaeng Inscription from the Sukhothai Period, which contains 11 words containing the letter.^[1] Additionally, there are a number of other similar inscriptions that contain the letter, including the Pa Nang Mo Inscription,^[2] the Pho Kun Ram Phon Inscription,^[3] the Kam Phaeng Ngam Inscription,^[4] and the Sadaeng Phon Kam Nam Su Nipphan Inscription.^[5]

Linguists believe that at the time kho khuat likely represented the velar fricative [x] and was originally distinguished from kho khai, which represents [k^h].^[6] Cognates of words beginning with kho khai and kho khuat in other Tai languages, such as Tai Dón, also consistently show different sounds. Later on, kho khuat gradually came to sound the same as kho khai, evidence of which may be seen from later inscriptions beginning to mix up the two letters.^[7]

Fall out of use

Both ฃ (kho khuat) and ฅ (kho khon) fell out of use at the same time when the first Thai-script typewriters were brought to Thailand in 1896, for there was no space for all characters in their 84 key keyboard. Thus these two letters, which at that point were already becoming rare, were chosen to be done away with. Even after the shift key was invented and the number of keys in typewriters was reduced to half, those two letters were not reinstated. They are, however, present on modern keyboards and are specified as part of the official standard.^[8] The reasons why precisely these two letters were chosen and not others is not known, but neither ฃ kho khuat nor ฅ kho khon correspond to letters of the Sanskrit or the Pali alphabet.^[9]