From The Collaborative International Dictionary of English v.0.48 :
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.
[1913 Webster]
Note: Heavy cavalry and light cavalry are so
distinguished by the character of their armament, and
by the size of the men and horses.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
cavalry
n 1: troops trained to fight on horseback; "500 horse led the
attack" [syn: cavalry, horse cavalry, horse]
2: a highly mobile army unit