American spelling vs US spelling

American spelling and US spelling both are nouns.

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

As nouns, American spelling and US spelling are synonyms defined as:

American spelling and US spelling: English orthography used in the United States (characterized by 'analyze', 'center', 'usable')

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