skeletal muscle vs musculus

skeletal muscle and musculus both are nouns.

Word	Noun	Adjective	Verb	Adverb
skeletal muscle	Yes	No	No	No
musculus	Yes	No	No	No

As nouns, musculus is a hypernym of skeletal muscle; that is, musculus is a word with a broader meaning than skeletal muscle:

skeletal muscle: a muscle that is connected at either or both ends to a bone and so move parts of the skeleton; a muscle that is characterized by transverse stripes
musculus: one of the contractile organs of the body

Other hypernyms of skeletal muscle include muscle.

skeletal muscle (noun)	musculus (noun)
a muscle that is connected at either or both ends to a bone and so move parts of the skeleton; a muscle that is characterized by transverse stripes	one of the contractile organs of the body