As a Noun: 1. A form of treatment in a hospital in which a doctor cuts open a patient's body in order to remove, replace, or repair a diseased or damaged part. English = operation, surgery. 2. A doctor who cuts open a patient's body in order to remove, replace, or repair a diseased or damaged part. English = surgeon. 3. A mark on the skin that is left after a wound has healed. English = scar. As a Verb or Adjective: 1. To cut open a patient's body in order to remove, replace, or repair a diseased or damaged part. English = operate, perform surgery.