occasion vs happening

occasion and happening both are nouns.

Word	Noun	Adjective	Verb	Adverb
occasion	Yes	No	Yes	No
happening	Yes	No	No	No

As nouns, happening is a hypernym of occasion; that is, happening is a word with a broader meaning than occasion:

Other hypernyms of occasion include natural event, occurrence, occurrent.

occasion (noun)	happening (noun)
an event that occurs at a critical time	an event that happens
a formal or official social gathering or ceremony of people
a rational motive for a belief or action
an opportunity to do something
the time of a particular event

occasion (verb)	happening (verb)
give occasion to