affair vs meeting

affair and meeting both are nouns.

Word	Noun	Adjective	Verb	Adverb
affair	Yes	No	No	No
meeting	Yes	No	No	No

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

affair (noun)	meeting (noun)
a vaguely specified concern	the social act of assembling for some common purpose
a formal or official social gathering or ceremony of people	the act of joining together as one
a usually secretive or illicit sexual relationship	a casual or unexpected convergence
	a formally arranged gathering
	a small informal social gathering
	a place where things merge or flow together (especially rivers)