social occasion vs assemblage

social occasion and assemblage both are nouns.

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

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

social occasion: a formal or official social gathering or ceremony of people
assemblage: a group of persons together in one place

Other hypernyms of social occasion include social event, gathering.

social occasion (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