operating theater vs American spelling

operating theater and American spelling both are nouns.

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

operating theater (noun)	American spelling (noun)
a room in a hospital equipped for the performance of surgical operations	English orthography used in the United States (characterized by 'analyze', 'center', 'usable')