buckskins vs knee pants

buckskins and knee pants both are nouns.

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

As nouns, knee pants is a hypernym of buckskins; that is, knee pants is a word with a broader meaning than buckskins:

Other hypernyms of buckskins include breeches, knee breeches, knickerbockers, knickers.

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