excuse vs ask for

excuse is a noun but ask for is not a noun.

Word	Noun	Adjective	Verb	Adverb
excuse	Yes	No	Yes	No
ask for	No	No	Yes	No

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

Other hypernyms of excuse include bespeak, call for, quest, request.

excuse (noun)	ask for (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)	ask for (verb)
accept an excuse for	express the need or desire for
defend, explain, clear away, or make excuses for by reasoning	increase the likelihood 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