I learned about the potlatch in 1959-ish, (all right, 1959 exactly) in a course dealing with (among other things) the Kwakiutl Indians, taught by one Clyde Kluckhohn, who should be authoritative. Is Chinook then the language-group of the Kwakiutl?

(The potlatch was described as an annual ritual during which the tribe gathered each year at the banks of the Columbia River to feast, and the wealthy of the tribe threw stuff into the river. Whoever threw away the most was declared the richest man in the tribe for that year. The word thus goes a step beyond Anu's posted definition -- not simply "lavish gifts," but extravagance and vanity to the point of folly, at least as seen through the filter of Western eyes.)