As a Noun: 1. The act of causing a living thing to die. English = killing. 2. A person who has killed someone. English = killer. 3. Anything that causes death to a person, animal or plant. English = killer. As a Verb or Adjective: 1. To cause a person, animal or plant to die. English = kill. 2. To kill a person in a violent way. Formal English = slay.