killer

n. murderer, one who kills, butcher

A killer is a person, animal, plant, object, etc., that kills. See also assassin; murderer.
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Killer Vox populi A person or thing that kills, in fact or figuratively. See Internet serial killer, Self-killer, Serial killer, Silent killer. [more]Killer - Community and Resources

Noun
1. someone who causes the death of a person or animal
(synonym) slayer
(hypernym) person, individual, someone, somebody, mortal, human, soul
(hyponym) executioner, public executioner
(derivation) kill
2. the causal agent resulting in death; "heart disease is the biggest killer in the United States"
(synonym) cause of death
(hypernym) causal agent, cause, causal agency
(derivation) kill
3. a difficulty that is hard to deal with; "that exam was a real killer"
(hypernym) difficulty
(derivation) kill
4. predatory black-and-white toothed whale with large dorsal fin; common in cold seas
(synonym) killer whale, orca, grampus, sea wolf, Orcinus orca
(hypernym) dolphin
(member-holonym) Orcinus, genus Orcinus

n. hit man, professional assassin, person who kills others for pay