line of defense vs American spelling

line of defense and American spelling both are nouns.

Word	Noun	Adjective	Verb	Adverb
line of defense	Yes	No	No	No
American spelling	Yes	No	No	No

line of defense (noun)	American spelling (noun)
defensive structure consisting of a barrier that can be employed for defense against attack	English orthography used in the United States (characterized by 'analyze', 'center', 'usable')
any organization whose responsibility it is to defend against something