gathering vs group action

gathering and group action both are nouns.

Word	Noun	Adjective	Verb	Adverb
gathering	Yes	No	No	No
group action	Yes	No	No	No

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

gathering (noun)	group action (noun)
the social act of assembling	action taken by a group of people
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