social occasion vs gathering

social occasion and gathering both are nouns.

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

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

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

Other hypernyms of social occasion include social event, assemblage.

social occasion (noun)	gathering (noun)
a formal or official social gathering or ceremony of people	the social act of assembling
	the act of gathering something
	sewing consisting of small folds or puckers made by pulling tight a thread in a line of stitching
	a group of persons together in one place