emergency room

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The section of a health care facility for providing rapid treatment to victims of sudden illness or trauma.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A department of a hospital primarily used for the treatment of the most serious, often life-threatening conditions.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a room in a hospital or clinic staffed and equipped to provide emergency care to persons requiring immediate medical treatment