galaxy vs aggregation

galaxy and aggregation both are nouns.

Word	Noun	Adjective	Verb	Adverb
galaxy	Yes	No	No	No
aggregation	Yes	No	No	No

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

galaxy: (astronomy) a collection of star systems; any of the billions of systems each having many stars and nebulae and dust
aggregation: several things grouped together or considered as a whole

Other hypernyms of galaxy include accumulation, assemblage, collection.

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

Other hypernyms of galaxy include accumulation, assemblage, collection.

galaxy (noun)	aggregation (noun)
(astronomy) a collection of star systems; any of the billions of systems each having many stars and nebulae and dust	the act of gathering something together
a splendid assemblage (especially of famous people)	several things grouped together or considered as a whole
tufted evergreen perennial herb having spikes of tiny white flowers and glossy green round to heart-shaped leaves that become coppery to maroon or purplish in fall