cubic millimeter vs American spelling

cubic millimeter and American spelling both are nouns.

Word	Noun	Adjective	Verb	Adverb
cubic millimeter	Yes	No	No	No
American spelling	Yes	No	No	No

cubic millimeter (noun)	American spelling (noun)
a metric measure of volume or capacity equal to a cube 1 millimeter on each edge	English orthography used in the United States (characterized by 'analyze', 'center', 'usable')