splint bone vs os

splint bone and os both are nouns.

Word	Noun	Adjective	Verb	Adverb
splint bone	Yes	No	No	No
os	Yes	No	No	No

As nouns, os is a hypernym of splint bone; that is, os is a word with a broader meaning than splint bone:

splint bone: a rudimentary metacarpal or metatarsal bone on either side of the cannon bone in the leg of a horse or related animal
os: rigid connective tissue that makes up the skeleton of vertebrates

Other hypernyms of splint bone include bone.

splint bone (noun)	os (noun)
a rudimentary metacarpal or metatarsal bone on either side of the cannon bone in the leg of a horse or related animal	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening