knee breeches vs knee pants

knee breeches and knee pants both are nouns.

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

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

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

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

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