From WordNet (r) 3.0 (2006) [wn]:
accordion
n 1: a portable box-shaped free-reed instrument; the reeds are
made to vibrate by air from the bellows controlled by the
player [syn: accordion, piano accordion, squeeze box]
From The Collaborative International Dictionary of English v.0.48 [gcide]: Accordion \Ac*cor"di*on\, n. [See Accord.] (Mus.) A small, portable, keyed wind instrument, whose tones are generated by play of the wind upon free metallic reeds. [1913 Webster]