category vs pigeonhole

category and pigeonhole both are nouns.

Word	Noun	Adjective	Verb	Adverb
category	Yes	No	No	No
pigeonhole	Yes	No	Yes	No

As nouns, pigeonhole is a hyponym of category; that is, pigeonhole is a word with a more specific, narrower meaning than category:

category: a general concept that marks divisions or coordinations in a conceptual scheme
pigeonhole: a specific (often simplistic) category

Other hyponyms of category include form, kind, sort, variety, rubric, way.

category (noun)	pigeonhole (noun)
a general concept that marks divisions or coordinations in a conceptual scheme	a small compartment
a collection of things sharing a common attribute	a specific (often simplistic) category

category (verb)	pigeonhole (verb)
	treat or classify according to a mental stereotype
	place into a small compartment