[4] Franciscan monks who traveled on Domingo Ramón's 1716–17 expedition through Texas founded Mission Nuestra Señora de los Dolores de los Ais;[5] however, the Eyeish were not generally accepting of Spanish missionary efforts.
[4] In the 18th century, the tribe contracted European diseases such as smallpox and measles from the French and Spanish explorers in the region.
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.
There is not 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.