pass off vs hap

pass off is not a noun while hap is a noun.

Word	Noun	Adjective	Verb	Adverb
pass off	No	No	Yes	No
hap	Yes	No	Yes	No

As verbs, pass off and hap are synonyms defined as:

Other synonyms of pass off include come about, fall out, go on, happen, occur, pass, take place.

pass off (noun)	hap (noun)
	an accidental happening

pass off (verb)	hap (verb)
expel (gases or odors)	come to pass
come to pass
disappear gradually
disregard
cause to be circulated and accepted in a false character or identity
be accepted as something or somebody in a false character or identity