the great unwashed vs masses

the great unwashed and masses both are nouns.

Word	Noun	Adjective	Verb	Adverb
the great unwashed	Yes	No	No	No
masses	Yes	No	No	No

As nouns, the great unwashed and masses are synonyms defined as:

Other synonyms of the great unwashed include hoi polloi, mass, multitude, people.

the great unwashed (noun)	masses (noun)
the common people generally	the common people generally