knee pants vs knee breeches

knee pants and knee breeches both are nouns.

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

As nouns, knee pants and knee breeches are synonyms defined as:

knee pants and knee breeches: (used in the plural) trousers ending above the knee

Other synonyms of knee pants include breeches, knickerbockers, knickers.

knee pants (noun)	knee breeches (noun)
(used in the plural) trousers ending above the knee	(used in the plural) trousers ending above the knee