leg bone vs os longum

leg bone and os longum both are nouns.

Word	Noun	Adjective	Verb	Adverb
leg bone	Yes	No	No	No
os longum	Yes	No	No	No

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

leg bone: a bone of the leg
os longum: in limbs of vertebrate animals: a long cylindrical bone that contains marrow

Other hypernyms of leg bone include long bone.

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