meeting vs affair

meeting and affair both are nouns.

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

As nouns, affair is a hypernym of meeting; that is, affair is a word with a broader meaning than meeting:

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