assembly vs group action

assembly and group action both are nouns.

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

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

assembly (noun)	group action (noun)
the social act of assembling	action taken by a group of people
the act of constructing something (as a piece of machinery)
a group of machine parts that fit together to form a self-contained unit
a public facility to meet for open discussion
a unit consisting of components that have been fitted together
a group of persons who are gathered together for a common purpose