mitigate vs excuse

mitigate is not a noun while excuse is a noun.

Word	Noun	Adjective	Verb	Adverb
mitigate	No	No	Yes	No
excuse	Yes	No	Yes	No

As verbs, excuse is a hypernym of mitigate; that is, excuse is a word with a broader meaning than mitigate:

Other hypernyms of mitigate include apologise, apologize, rationalise, rationalize.

mitigate (noun)	excuse (noun)
	a poor example
	a defense of some offensive behavior or some failure to keep a promise etc.
	a note explaining an absence

mitigate (verb)	excuse (verb)
to temper	accept an excuse for
lessen or to try to lessen the seriousness or extent of	defend, explain, clear away, or make excuses for by reasoning
	excuse, overlook, or make allowances for; be lenient with
	serve as a reason or cause or justification of
	grant exemption or release to
	ask for permission to be released from an engagement