alteration vs happening

alteration and happening both are nouns.

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

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

alteration: an event that occurs when something passes from one state or phase to another
happening: an event that happens

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

alteration (noun)	happening (noun)
the act of revising or altering (involving reconsideration and modification)	an event that happens
the act of making something different (as e.g. the size of a garment)
an event that occurs when something passes from one state or phase to another