breeches buoy vs life buoy

breeches buoy and life buoy both are nouns.

Word	Noun	Adjective	Verb	Adverb
breeches buoy	Yes	No	No	No
life buoy	Yes	No	No	No

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

breeches buoy: a life buoy in the form of a ring with short breeches for support; used to transfer people from a ship
life buoy: a life preserver in the form of a ring of buoyant material

Other hypernyms of breeches buoy include life belt, life ring, lifesaver.

breeches buoy (noun)	life buoy (noun)
a life buoy in the form of a ring with short breeches for support; used to transfer people from a ship	a life preserver in the form of a ring of buoyant material