event vs happening

event and happening both are nouns.

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

As nouns, happening is a hyponym of event; that is, happening is a word with a more specific, narrower meaning than event:

event (noun)	happening (noun)
something that happens at a given place and time	an event that happens
a phenomenon located at a single point in space-time; the fundamental observational entity in relativity theory
a phenomenon that follows and is caused by some previous phenomenon
a special set of circumstances