a doctor who works in a hospital in casualty (= the hospital department where people who are hurt in accidents or suddenly become ill go for urgent treatment) and is trained to deal with accidents or sudden illness: It was my day off after a busy week as a casualty officer in an inner-city hospital. A casualty is a loss resulting from an accident or someone who is hurt, wounded, diseased, detained or dead in an accident. The term casualty means a seriously injured patient.