crowd together vs mass

crowd together is not a noun while mass is a noun.

Word	Noun	Adjective	Verb	Adverb
crowd together	No	No	Yes	No
mass	Yes	Yes	Yes	No

As verbs, mass is a hyponym of crowd together; that is, mass is a word with a more specific, narrower meaning than crowd together:

Other hyponyms of crowd together include overcrowd, pour, pullulate, stream, swarm, teem, herd, jam, mob, pack, pile, throng.

crowd together (noun)	mass (noun)
	the property of a body that causes it to have weight in a gravitational field
	the property of something that is great in magnitude
	the common people generally
	an ill-structured collection of similar things (objects or people)
	a body of matter without definite shape
	(often followed by `of') a large number or amount or extent

crowd together (adjective)	mass (adjective)
	formed of separate units gathered into a mass or whole

crowd together (verb)	mass (verb)
to gather together in large numbers	join together into a mass or collect or form a mass