plus fours vs breeches

plus fours and breeches both are nouns.

Word	Noun	Adjective	Verb	Adverb
plus fours	Yes	No	No	No
breeches	Yes	No	No	No

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

plus fours: men's baggy knickers hanging below the knees; formerly worn for sports (especially golf)
breeches: (used in the plural) trousers ending above the knee

Other hypernyms of plus fours include knee breeches, knee pants, knickerbockers, knickers.

plus fours (noun)	breeches (noun)
men's baggy knickers hanging below the knees; formerly worn for sports (especially golf)	(used in the plural) trousers ending above the knee