buckskins vs knee breeches

buckskins and knee breeches both are nouns.

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

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

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

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