convention vs gathering

convention and gathering both are nouns.

Word	Noun	Adjective	Verb	Adverb
convention	Yes	No	No	No
gathering	Yes	No	No	No

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

Other hypernyms of convention include assemblage, assembly.

convention (noun)	gathering (noun)
the act of convening	the social act of assembling
orthodoxy as a consequence of being conventional	the act of gathering something
something regarded as a normative example	sewing consisting of small folds or puckers made by pulling tight a thread in a line of stitching
(diplomacy) an international agreement	a group of persons together in one place
a large formal assembly