lateral rectus vs eye muscle

lateral rectus and eye muscle both are nouns.

Word	Noun	Adjective	Verb	Adverb
lateral rectus	Yes	No	No	No
eye muscle	Yes	No	No	No

As nouns, eye muscle is a hypernym of lateral rectus; that is, eye muscle is a word with a broader meaning than lateral rectus:

lateral rectus: the ocular muscle whose contraction turns the eyeball outward
eye muscle: one of the small muscles of the eye that serve to rotate the eyeball

Other hypernyms of lateral rectus include ocular muscle.

lateral rectus (noun)	eye muscle (noun)
the ocular muscle whose contraction turns the eyeball outward	one of the small muscles of the eye that serve to rotate the eyeball