nuclear club vs aggregation

nuclear club and aggregation both are nouns.

Word	Noun	Adjective	Verb	Adverb
nuclear club	Yes	No	No	No
aggregation	Yes	No	No	No

As nouns, aggregation is a hypernym of nuclear club; that is, aggregation is a word with a broader meaning than nuclear club:

Other hypernyms of nuclear club include accumulation, assemblage, collection.

nuclear club (noun)	aggregation (noun)
the nations possessing nuclear weapons	the act of gathering something together
	several things grouped together or considered as a whole