contusion vs ecchymosis

contusion and ecchymosis both are nouns.

Word	Noun	Adjective	Verb	Adverb
contusion	Yes	No	No	No
ecchymosis	Yes	No	No	No

As nouns, ecchymosis is a hyponym of contusion; that is, ecchymosis is a word with a more specific, narrower meaning than contusion:

contusion: an injury that doesn't break the skin but results in some discoloration
ecchymosis: the purple or black-and-blue area resulting from a bruise

Other hyponyms of contusion include petechia, black eye, mouse, shiner.

contusion (noun)	ecchymosis (noun)
the action of bruising	the escape of blood from ruptured blood vessels into the surrounding tissue to form a purple or black-and-blue spot on the skin
an injury that doesn't break the skin but results in some discoloration	the purple or black-and-blue area resulting from a bruise