Thai people (ชาวไทย; endonym), Central Thai people (คนภาคกลาง; exonym and also domestically), Southern Thai people (คนใต้; exonym and also domestically), Dambro (ตามโพร), Siamese (ชาวสยาม; historical exonym and sometimes domestically), Tai Noi people (ไทน้อย; historical endonym and sometimes domestically), Thai Siam (ไทยสยาม), are a Southeast Asian ethnic group native to Thailand. In a narrower sense, the Thais are also a Tai ethnic group dominant in Central and Southern Thailand (Siam proper). Part of the larger Tai ethno-linguistic group native to Southeast Asia as well as Southern China and Northeast India, Thais speak the Sukhothai languages (Central Thai and Southern Thai language), which is classified as part of the Kra–Dai family of languages. The majority of Thais are followers of Theravada Buddhism.
As a result of government policy during the 1930s and 1940s resulting in successful forced assimilation of many the various ethno-linguistic groups in the country into the dominant Central Thai language and culture, the term Thai people has come to refer to the population of Thailand in general. This includes other subgroups of the Tai ethno-linguistic group, such as the Yuan people and the Isan people, as well as non-Southeast Asian and non-Tai groups, the largest of which is that of the Han Chinese, who form a substantial minority ethnic group in Thailand.
Tai languages and Thai language
According to Michel Ferlus, the ethnonyms Thai/Tai (or Thay/Tay) would have evolved from the etymon *k(ə)ri: 'human being' through the following chain: *kəri: > *kəli: > *kədi:/*kədaj > *di:/*daj > *dajA (Proto-Southwestern Tai) > thajA2 (in Siamese and Lao) or > tajA2 (in the other Southwestern and Central Tai languages classified by Li Fangkuei). Michel Ferlus' work is based on some simple rules of phonetic change observable in the Sinosphere and studied for the most part by William H. Baxter (1992).
Michel Ferlus notes that a deeply rooted belief in Thailand has it that the term "Thai" derives from the last syllables -daya in Sukhodaya/ Sukhothay (สุโขทัย), the name of the Sukhothai Kingdom.