Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

accordion
     n : a portable box-shaped free-reed instrument; the reeds are
         made to vibrate by air from the bellows controlled by the
         player [syn: {piano accordion}, {squeeze box}]

accordion
     adj : arranged in parallel folds; "plicate leaves" [syn: {plicate}]