fetter bone vs os

fetter bone and os both are nouns.

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

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

Other hypernyms of fetter bone include bone.

fetter bone (noun)	os (noun)
the part between the fetlock and the hoof	rigid connective tissue that makes up the skeleton of vertebrates
	a mouth or mouthlike opening