pigeonholing vs grouping

pigeonholing and grouping both are nouns.

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

As nouns, pigeonholing and grouping are synonyms defined as:

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