lackluster vs American spelling

lackluster is not a noun while American spelling is a noun.

Word	Noun	Adjective	Verb	Adverb
lackluster	No	Yes	No	No
American spelling	Yes	No	No	No

lackluster (noun)	American spelling (noun)
	English orthography used in the United States (characterized by 'analyze', 'center', 'usable')

lackluster (adjective)	American spelling (adjective)
lacking luster or shine
lacking brilliance or vitality