excuse vs mitigate

excuse is a noun but mitigate is not a noun.

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

As verbs, mitigate is a hyponym of excuse; that is, mitigate is a word with a more specific, narrower meaning than excuse:

Other hyponyms of excuse include color, colour, gloss, plead, extenuate, palliate.

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

excuse (verb)	mitigate (verb)
accept an excuse for	to temper
defend, explain, clear away, or make excuses for by reasoning	lessen or to try to lessen the seriousness or extent of
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