nerve fiber vs American spelling

nerve fiber and American spelling both are nouns.

Word	Noun	Adjective	Verb	Adverb
nerve fiber	Yes	No	No	No
American spelling	Yes	No	No	No

nerve fiber (noun)	American spelling (noun)
a threadlike extension of a nerve cell	English orthography used in the United States (characterized by 'analyze', 'center', 'usable')