emergency

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

• noun A serious situation or occurrence that happens unexpectedly and demands immediate action.
• noun A condition of urgent need for action or assistance.
• adjective For use during emergencies.

from The Century Dictionary.

• noun Same as emergence, 1.
• noun A sudden or unexpected happening; an unforeseen occurrence or condition; specifically, a perplexing contingency or complication of circumstances.
• noun A sudden or unexpected occasion for action; exigency; pressing necessity.
• noun Something not calculated upon; an unexpected gain; a casual profit.
• noun Synonyms Crisis, etc. (see exigency); pinch, strait.
• Pertaining to or provided for an emergency; dealing with or for use in emergencies: as, an emergency man; an emergency wagon.

from the GNU version of the Collaborative International Dictionary of English.

• noun Sudden or unexpected appearance; an unforeseen occurrence; a sudden occasion.
• noun An unforeseen occurrence or combination of circumstances which calls for immediate action or remedy; pressing necessity; exigency.

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

• noun A situation such as a natural or man-made disaster requiring urgent assistance.
• noun Canada, US The department of a hospital that treats emergencies.
• noun archaic The quality of being emergent; sudden or unexpected appearance; an unforeseen occurrence.
• adjective Related to the emergency or to the provision of assistance.

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

• noun a state in which martial law applies
• noun a brake operated by hand; usually operates by mechanical linkage
• noun a sudden unforeseen crisis (usually involving danger) that requires immediate action