muscle is a noun.
muscles is a plural noun.
ex:
Her muscles tensed when she saw her ex boyfriend.
Broca's area
Broca's area
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
what part of speech is beneath
adverb
Muscle builder is a noun. It names a type of person.
The part of speech for "explicit" is an adjective.
The part of speech for "lecturer" is a noun.
The part of speech for "rapid" is an adjective.
The part of speech of "came" is a verb.