black eye vs happening

black eye and happening both are nouns.

Word	Noun	Adjective	Verb	Adverb
black eye	Yes	No	No	No
happening	Yes	No	No	No

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

black eye: an unfortunate happening that hinders or impedes; something that is thwarting or frustrating
happening: an event that happens

Other hypernyms of black eye include natural event, occurrence, occurrent.

black eye (noun)	happening (noun)
an unfortunate happening that hinders or impedes; something that is thwarting or frustrating	an event that happens
a swollen bruise caused by a blow to the eye
a bad reputation