"killer" in the noun sense

1. killer, slayer

someone who causes the death of a person or animal

2. cause of death, killer

the causal agent resulting in death

"heart disease is the biggest killer in the United States"

3. killer

a difficulty that is hard to deal with

"that exam was a real killer"

4. killer whale, killer, orca, grampus, sea wolf, Orcinus orca

predatory black-and-white toothed whale with large dorsal fin common in cold seas

Source: WordNet® (An amazing lexical database of English)

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