success vs happening

success and happening both are nouns.

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

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

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

success (noun)	happening (noun)
an attainment that is successful	an event that happens
an event that accomplishes its intended purpose
a person with a record of successes
a state of prosperity or fame