/ ˈkɪlə(r); NAmE / noun
1.
a person, an animal or a thing that kills :
Police are hunting his killer.
Heart disease is the biggest killer in Scotland.
an electric insect killer
The players lacked the killer instinct .
—see also ladykiller , serial killer
2.
( informal ) something that is very difficult, very exciting or very skilful :
The exam was a real killer.
The new movie is a killer.