long bone vs arm bone

long bone and arm bone both are nouns.

Word	Noun	Adjective	Verb	Adverb
long bone	Yes	No	No	No
arm bone	Yes	No	No	No

As nouns, arm bone is a hyponym of long bone; that is, arm bone is a word with a more specific, narrower meaning than long bone:

long bone: in limbs of vertebrate animals: a long cylindrical bone that contains marrow
arm bone: a bone in the arm

Other hyponyms of long bone include epiphysis, diaphysis, shaft, leg bone.

long bone (noun)	arm bone (noun)
in limbs of vertebrate animals: a long cylindrical bone that contains marrow	a bone in the arm