occur vs hap

occur is not a noun while hap is a noun.

Word	Noun	Adjective	Verb	Adverb
occur	No	No	Yes	No
hap	Yes	No	Yes	No

As verbs, occur and hap are synonyms defined as:

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

occur (noun)	hap (noun)
	an accidental happening

occur (verb)	hap (verb)
come to pass	come to pass
come to one's mind; suggest itself
to be found to exist