muscle fiber vs muscle fibre

muscle fiber and muscle fibre both are nouns.

Word	Noun	Adjective	Verb	Adverb
muscle fiber	Yes	No	No	No
muscle fibre	Yes	No	No	No

As nouns, muscle fiber and muscle fibre are synonyms defined as:

muscle fiber and muscle fibre: an elongated contractile cell that forms the muscles of the body

Other synonyms of muscle fiber include muscle cell.

muscle fiber (noun)	muscle fibre (noun)
an elongated contractile cell that forms the muscles of the body	an elongated contractile cell that forms the muscles of the body