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