1825-35, Americanism; assimilated variant of earlier chitmunk, apparently < Ojibwaačitamo·nʔ red squirrel, equivalent to ačit- headfirst, face-down + derivational elements; so called from the squirrel's manner of descending trees
1841, from Algonquian, probably Ojibwa ajidamoo (in the Ottawa dialect ajidamoonh) "red squirrel," lit. "one who descends trees headlong" (containing ajid- "upside down"), probably infl. by Eng. chip and mink.