operating theater vs operating room

operating theater and operating room both are nouns.

Word	Noun	Adjective	Verb	Adverb
operating theater	Yes	No	No	No
operating room	Yes	No	No	No

As nouns, operating theater and operating room are synonyms defined as:

operating theater and operating room: a room in a hospital equipped for the performance of surgical operations

Other synonyms of operating theater include operating theatre, OR, surgery.

operating theater (noun)	operating room (noun)
a room in a hospital equipped for the performance of surgical operations	a room in a hospital equipped for the performance of surgical operations