muscle vs musculus

muscle and musculus both are nouns.

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

As nouns, muscle and musculus are synonyms defined as:

muscle (noun)	musculus (noun)
possessing muscular strength	one of the contractile organs of the body
authority or power or force (especially when used in a coercive way)
one of the contractile organs of the body
animal tissue consisting predominantly of contractile cells
a bully employed as a thug or bodyguard

muscle (verb)	musculus (verb)
make one's way by force