Source : Webster's Revised Unabridged Dictionary (1913)

Cavalry \Cav"al*ry\, n. [F. cavalerie, fr. It. cavalleria. See
   {Cavalier}, and cf. {chivalry}.] (Mil.)
   That part of military force which serves on horseback.

   Note: {Heavy cavalry} and {light cavalry} are so
         distinguished by the character of their armament, and
         by the size of the men and horses.

Source : WordNet®

cavalry
     n 1: troops trained to fight on horseback; "500 horse led the
          attack" [syn: {horse cavalry}, {horse}]
     2: a highly mobile army unit