killer killer /ˈkɪlɝ/

noun

1. () Someone who causes the death of a person or animal  ( slayer , killer )
   someone who causes the death of a person or animal
     The notorious killer left behind a trail of gruesome crimes.
   The notorious killer left behind a trail of gruesome crimes.
   
   
2. Predatory black-and-white toothed whale with large dorsal fin; common in cold seas  ( grampus , killer , killer whale , orca , Orcinus orca , sea wolf )
   predatory black-and-white toothed whale with large dorsal fin; common in cold seas
   
   
3. A difficulty that is hard to deal with  ( killer )
   a difficulty that is hard to deal with
    That exam was a real killer
   that exam was a real killer
   
4. The causal agent resulting in death  ( cause of death , killer )
   the causal agent resulting in death
    Heart disease is the biggest killer in the United States
   heart disease is the biggest killer in the United States