casualty
Casualty (noun) means an unlucky event that occurs unexpectedly, such as an accident or disaster.
Etymology
From casual, from Middle French casuel, from Medieval Latin casualitas and Late Latin cāsuālis (“happening by chance”), from Latin cāsus (“event”) (English case), from cadere (“to fall”). Originally meaning “a chance event” (compare casual, as in “casual encounter”), it developed a negative meaning as “an unfortunate event”, especially the loss of a person.