The word texas (tejas, tayshas, texias, thecas, techan, teysas, techas) was widely used among Indians in Texas and is a huge contributing factor in the Lone Star State's modern day name.
The Hasinais most likely used the word "tejas" as a form of greeting, or another way to say "Hello, friend." This was used to greet other friendly Tribes with which the Hasinais were allies.
When the word had reached the Spanish, the term most likely changed to the modern day spelling of "Texas" in the year 1689 according to the Texas State Historical Association.
Caddo, from which the word tejas derived, was the common language among the Caddo Nation. The Caddo language is critically endangered to this day with only 25 speakers left in 2009.