knee pants vs buckskins

knee pants and buckskins both are nouns.

Word	Noun	Adjective	Verb	Adverb
knee pants	Yes	No	No	No
buckskins	Yes	No	No	No

As nouns, buckskins is a hyponym of knee pants; that is, buckskins is a word with a more specific, narrower meaning than knee pants:

Other hyponyms of knee pants include britches, plus fours, trunk hose.

knee pants (noun)	buckskins (noun)
(used in the plural) trousers ending above the knee	(used in the plural) breeches made of buckskin