1A member of a Cree people inhabiting the shores of Lac Mistassini in south central Quebec. Frequently attributive, especially in "Mistassini Cree", "Mistassini Indian".
2The language of the Mistassini, a dialect of East Cree.
Late 18th century; earliest use found in New & Accurate Map Quebec. From Canadian French Mistassins, plural, shortened from Old Montagnais mistasini:waky, lit. ‘people of the great rock’, referring to a large rock in Lac Mistassini, called in Mistassini East Cree mistasiniy, mistasinii great stone, which is also the name of Mistassini Post.