American English vs fourth

American English and fourth both are nouns.

Word	Noun	Adjective	Verb	Adverb
American English	Yes	No	No	No
fourth	Yes	Yes	No	Yes

American English (noun)	fourth (noun)
the English language as used in the United States	the musical interval between one note and another four notes away from it
	one of four equal parts
	following the third position; number four in a countable series

American English (adjective)	fourth (adjective)
	coming next after the third and just before the fifth in position or time or degree or magnitude

American English (adverb)	fourth (adverb)
	in the fourth place