American spelling vs spelling

American spelling and spelling both are nouns.

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

As nouns, spelling is a hypernym of American spelling; that is, spelling is a word with a broader meaning than American spelling:

American spelling: English orthography used in the United States (characterized by 'analyze', 'center', 'usable')
spelling: forming words with letters according to the principles underlying accepted usage

American spelling (noun)	spelling (noun)
English orthography used in the United States (characterized by 'analyze', 'center', 'usable')	forming words with letters according to the principles underlying accepted usage