knickers vs britches

knickers and britches both are nouns.

Word	Noun	Adjective	Verb	Adverb
knickers	Yes	No	No	No
britches	Yes	No	No	No

As nouns, britches is a hyponym of knickers; that is, britches is a word with a more specific, narrower meaning than knickers:

Other hyponyms of knickers include buckskins, plus fours, trunk hose.

knickers (noun)	britches (noun)
(used in the plural) underpants worn by women	(used in the plural) informal term for breeches
(used in the plural) trousers ending above the knee