hind leg vs hind limb

hind leg and hind limb both are nouns.

Word	Noun	Adjective	Verb	Adverb
hind leg	Yes	No	No	No
hind limb	Yes	No	No	No

As nouns, hind limb is a hypernym of hind leg; that is, hind limb is a word with a broader meaning than hind leg:

hind leg: the back limb of a quadruped
hind limb: a posterior appendage such as a leg or the homologous structure in other animals

Other hypernyms of hind leg include hindlimb.

hind leg (noun)	hind limb (noun)
the back limb of a quadruped	a posterior appendage such as a leg or the homologous structure in other animals