petechia vs contusion

petechia and contusion both are nouns.

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

As nouns, contusion is a hypernym of petechia; that is, contusion is a word with a broader meaning than petechia:

petechia: a minute red or purple spot on the surface of the skin as the result of tiny hemorrhages of blood vessels in the skin (as in typhoid fever)
contusion: an injury that doesn't break the skin but results in some discoloration

Other hypernyms of petechia include bruise.

petechia (noun)	contusion (noun)
a minute red or purple spot on the surface of the skin as the result of tiny hemorrhages of blood vessels in the skin (as in typhoid fever)	the action of bruising
	an injury that doesn't break the skin but results in some discoloration