social affair vs assemblage

social affair and assemblage both are nouns.

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

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

Other hypernyms of social affair include social event, gathering.

social affair (noun)	assemblage (noun)
a formal or official social gathering or ceremony of people	the social act of assembling
	a system of components assembled together for a particular purpose
	a group of persons together in one place
	several things grouped together or considered as a whole