The Collaborative International Dictionary of English v.0.48:

Ecchymosis \Ec`chy*mo"sis\, n.; pl. Ecchymoses. [NL., fr. Gr.
   ?, fr. ? to extravasate; 'ek out of + ? to pour.] (Med.)
   A livid or black and blue spot, produced by the extravasation
   or effusion of blood into the areolar tissue from a
   contusion.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ecchymosis
    n 1: the purple or black-and-blue area resulting from a bruise
    2: the escape of blood from ruptured blood vessels into the
       surrounding tissue to form a purple or black-and-blue spot on
       the skin

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

ECCHYMOSIS, med. jur. Blackness. It is an extravasation of blood by rupture
of capillary vessels, and hence it follows contusion; but it may exist, as
in cases of scurvy, and other morbid conditions, without the latter. Ryan's
Med. Jur. 172.