Definition from Wiktionary, the free dictionary
casualty (plural casualties)
- (obsolete) Chance nature; randomness.
- Something that happens by chance, especially an unfortunate event; an accident, a disaster.
- A person suffering from injuries or who has been killed due to an accident or through an act of violence.
- (UK) The accident and emergency department of a hospital.
(hospital's accident and emergency):
- emergency / emergency room / emergency department / emergency ward / E. R./E.R./ER
- casualty department / casualty ward
- accident and emergency / A&E
an accident, a disaster