Learner's definition of CASUALTY
1 [count] : a person who is hurt or killed during an accident, war, etc.
a low number of casualties
The army suffered/took/sustained heavy casualties [=many soldiers were killed or wounded] in the town.
casualty rates [=the number of people or wounded killed each day]
2 [count] : a person or thing that is harmed, lost, or destroyed : victim — usually + of