masses vs grouping

masses and grouping both are nouns.

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

As nouns, grouping is a hypernym of masses; that is, grouping is a word with a broader meaning than masses:

Other hypernyms of masses include group.

masses (noun)	grouping (noun)
the common people generally	any number of entities (members) considered as a unit
	the activity of putting things together in groups
	a system for classifying things into groups