Sinixt (snsəlxcín) is one of multiple distinct dialects of the Colville-Okanagan language. It is part of the Southern Interior Salish sub-grouping of the Salishan Language family. Traditionally spoken among the Sinixt People of the southern Interior Plateau region and based primarily in the Columbia River Basin, it is closely related to other Interior Salish languages and dialects. As of 2022, it had around 30 first-language speakers.

Six of the twelve tribes which make up the Colville Confederated Tribes speak Sinixt:

Linguists named Salishan Plateau languages based in the land on which they are spoken, and, since colonization and the relocation of Interior Salish families, the differences between these languages are not as well-known today, and a more generalized language has come into use. However, the Sinixt Nation, an unrecognized First Nation in Canada states on its website that it wishes to preserve the language with its unique dialectic differences, as exactly as possible, no matter how insignificant the pronunciation differences may be between the various dialects. The Sinixt also "encourage people working to save the language to respect these dialects whenever possible and to honor them."

The Sinixt Nation website also states that "originally there were two versions of the language for Sinixt peoples, one for the men (snskəlxʷcín or language of humans) and one for the women (snsəlxcín or language of water). Both of these dialects were understood by all Sinixt people but reserved for speaking only by the determined sex." The language used today "is a combination of the two."

Scottish-Canadian anthropologist James Teit noted in 1909 that the Sinixt dialect was distinguished from other Plateau Salishan dialects by the slow and measured manner in which it was spoken. f

The endonym n̓səl̓xčin̓, also written as n̓syil̓xčn̓ or nsyilxcn, is derived from the word sil̓x, which can also be spelled syil̓x or syilx. Sil̓x means "Salish people" and does not refer to a specific band. It is used to refer to all Salish people, but especially Sinixt speakers. The addition of n̓– čin̓, n̓–čn̓ or n–cn turns the word into n̓səl̓xčin̓, meaning "Salish people's language".

Randy Bouchard and Dorothy Kennedy record fur trader Alexander Ross as the first person "to record an identification of the Lakes (Sinixt) people" by a transcription of their name, in September 1821."

Anthropologists Franz Boas, James Teit and Verne Ray, and explorers George Mercer Dawson, James Turnbull, and Walter Moberly (engineer) all added to the extant written record of Sinixt words and place names