mass vs masses

mass and masses both are nouns.

Word	Noun	Adjective	Verb	Adverb
mass	Yes	Yes	Yes	No
masses	Yes	No	No	No

As nouns, mass and masses are synonyms defined as:

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

mass (noun)	masses (noun)
the property of a body that causes it to have weight in a gravitational field	the common people generally
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

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

mass (verb)	masses (verb)
join together into a mass or collect or form a mass