Karankawa is the extinct, unclassified language of the Texan coast, where the Karankawa people migrated between the mainland and the barrier islands. It was not closely related to other known languages in the area, much of which are also poorly attested, and may have been a language isolate

Language isolate

A language isolate, in the absolute sense, is a natural language with no demonstrable genealogical relationship with other languages; that is, one that has not been demonstrated to descend from an ancestor common with any other language. They are in effect language families consisting of a single...

. A couple hundred words are preserved, collected in 1698, 1720, and 1828; in the 1880s, three lists were collected from non-Karankawa who knew some words.

Karankawa has sometimes been included with neighboring languages in a Coahuiltecan

Coahuiltecan

Coahuiltecan or Paikawa was a proposed language family in John Wesley Powell's 1891 classification of Native American languages that consisted of Coahuilteco and Cotoname. The proposal was expanded to include Comecrudo, Karankawa, and Tonkawa...

family, but that is now thought to be spurious.