triad vs gathering

triad and gathering both are nouns.

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

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

Other hypernyms of triad include assemblage.

triad (noun)	gathering (noun)
a three-note major or minor chord; a note and its third and fifth tones	the social act of assembling
three people considered as a unit	the act of gathering something
a set of three similar things considered as a unit	sewing consisting of small folds or puckers made by pulling tight a thread in a line of stitching
the cardinal number that is the sum of one and one and one	a group of persons together in one place