From The Collaborative International Dictionary of English v.0.48 :
Chipmunk \Chip"munk`\, n. [Indian name.] (Zool.) A squirrel-like animal of the genus Tamias, sometimes called the striped squirrel, chipping squirrel, ground squirrel, hackee. The common species of the United States is the Tamias striatus. [Written also chipmonk, chipmuck, and chipmuk.] [1913 Webster]From WordNet (r) 3.0 (2006) :
chipmunk n 1: a burrowing ground squirrel of western America and Asia; has cheek pouches and a light and dark stripe running down the body