Although the Eyeish people were clearly connected to the Caddo people politically, it is not clear what language they spoke nor how that language relates genealogically to other known languages. Explorer John Sibley wrote that the Eyeish language was one of three unique languages spoken by the Eyeish, the
Adai and the
Yatasi and
Natchitoches people and that Eyeish was spoken by no other group: ‘[it] differs from all other, and is so difficult to speak or understand, that no nation can speak ten words of it.’ He collected a wordlist in 1807 for
Thomas Jefferson, but this was lost when a thief stole Jefferson's linguistic papers as they were being moved from Washington, DC to Monticello in Jefferson's second term. Sibley also reported that the Eyeish and Adai were bilingual in Caddo, which was used as a
contact language. However, according to informant Caddo Jake's report to
John R. Swanton, Eyeish was mutually intelligible with the Adai language. There is no sufficient evidence to conclusively relate Adai to
Caddoan languages, the only documentation being a list of 275 words compiled by Sibley. Allan Taylor and Alexander Lesser and Gene Weltfish have speculated that Adai belonged to the Caddoan language family and was possibly a dialect of Caddo. ==Notes==