fess up vs confess

fess up and confess both are verbs.

Word	Noun	Adjective	Verb	Adverb
fess up	No	No	Yes	No
confess	No	No	Yes	No

As verbs, confess is a hypernym of fess up; that is, confess is a word with a broader meaning than fess up:

Other hypernyms of fess up include concede, profess.

fess up (verb)	confess (verb)
admit or acknowledge a wrongdoing or error	confess to a punishable or reprehensible deed, usually under pressure
	admit (to a wrongdoing)
	confess to God in the presence of a priest, as in the Catholic faith