leg bone vs femur

leg bone and femur both are nouns.

Word	Noun	Adjective	Verb	Adverb
leg bone	Yes	No	No	No
femur	Yes	No	No	No

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

leg bone: a bone of the leg
femur: the longest and thickest bone of the human skeleton; extends from the pelvis to the knee

Other hyponyms of leg bone include femoris, thighbone, calf bone, fibula, shin, shin bone, shinbone, tibia.

leg bone (noun)	femur (noun)
a bone of the leg	the longest and thickest bone of the human skeleton; extends from the pelvis to the knee