cubic kilometer vs American spelling

cubic kilometer and American spelling both are nouns.

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

cubic kilometer (noun)	American spelling (noun)
a unit of capacity equal to the volume of a cube one kilometer on each edge	English orthography used in the United States (characterized by 'analyze', 'center', 'usable')