US English spelling vs American English spelling

US English spelling and American English spelling both are nouns.

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

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

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

Other synonyms of US English spelling include American English orthography, American spelling, US English orthography, US spelling.

US English spelling (noun)	American English 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')