social gathering vs social affair

social gathering and social affair both are nouns.

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

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

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

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

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