breeches vs knee pants

breeches and knee pants both are nouns.

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

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

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

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

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