social affair vs social gathering

social affair and social gathering both are nouns.

Word	Noun	Adjective	Verb	Adverb
social affair	Yes	No	No	No
social gathering	Yes	No	No	No

As nouns, social affair and social gathering are synonyms defined as:

social affair and social gathering: a formal or official social gathering or ceremony of people

Other synonyms of social affair include affair, function, occasion, social function, social occasion.

social affair (noun)	social gathering (noun)
a formal or official social gathering or ceremony of people	a formal or official social gathering or ceremony of people