The Collaborative International Dictionary of English v.0.48:

Contusion \Con*tu"sion\ (k[o^]n*t[=u]"zh[u^]n), n. [L. contusio:
   cf. F. contusion.]
   1. The act or process of beating, bruising, or pounding; the
      state of being beaten or bruised.
      [1913 Webster]

   2. (Med.) A bruise; an injury attended with more or less
      disorganization of the subcutaneous tissue and effusion of
      blood beneath the skin, but without apparent wound.
      [1913 Webster]

WordNet (r) 3.0 (2006):

contusion
    n 1: an injury that doesn't break the skin but results in some
         discoloration [syn: bruise, contusion]
    2: the action of bruising; "the bruise resulted from a
       contusion"

Bouvier's Law Dictionary, Revised 6th Ed (1856):

CONTUSION, med. jurisp. An injury or lesion, arising from the shock of a
body with a large surface, which presents no loss of substance, and no
apparent wound. If the skin be divided, the injury takes the name of a
contused wound. Vide 1 Ch. Pr, 38; 4 Carr. & P. 381, 487, 558, 565; 6 Carr.
& P. 684; 2 Beck's Med. Jur. 178.