killer

American  

[kil-er] / ˈkɪl ər /

noun

• killers
  plural

1. a person or thing that kills.

2. killer whale.

3. a device used by a post office for printing cancellations on postage stamps.

4. a mark of cancellation made on a postage stamp.

5. Slang. something or someone having a formidable impact, devastating effect, etc..

   The math test was a real killer.

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adjective

Slang.

1. severe; powerful.

   a killer cold.

2. very difficult or demanding.

   a killer chess tournament.

3. highly effective; superior.

   a killer recipe for fried chicken.

killer British  

/ ˈkɪlə /

noun

1. 1. a person or animal that kills, esp habitually

   2. ( as modifier )

      a killer shark

2. something, esp a task or activity, that is particularly taxing or exhausting

3. an animal selected to be slaughtered for food

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Usage

What is a basic definition of killer? A killer is a person or thing that kills, meaning they end lives. Killer is also used in slang to mean something that is devastating or exhausting. Additionally, killer is used in slang to describe something as severe or powerful. Killer has several other meanings as a noun and an adjective. A person or thing that ends someone’s life is a killer. In terms of a person, killer is often used interchangeably with murderer. However, killer can refer to someone who killed another person by accident, while murderer is not used in that sense.

• Real-life examples: John Wilkes Booth was Abraham Lincoln’s killer. Jack the Ripper was an infamous killer. Bacteria and viruses often act as natural killers. People use weed killers on their lawns.
• Used in a sentence: My cat is a very effective killer of birds.

In slang, killer is used to describe something as causing stress, exhaustion, pain, or misery.

• Real-life examples: You might call a particularly hard test a killer test. A killer workout would push your body to the limits of its abilities.
• Used in a sentence: That history assignment turned out to be a killer and took me forever to finish.

In slang, killer is also used to describe something as severe, intense, or powerful.

• Real-world examples: You might call a baseball game that goes into extra innings with a 2–2 score, a killer game. If you come down with a severe cold that keeps you in bed for several days, you could call it a killer cold.
• Used in a sentence: After living abroad for five years, Michelle came down with a killer case of homesickness.

Other Word Forms

Derived Forms

• self-killer
  noun

Inflected Forms

Nouns

• killers
  plural

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Etymology

Origin of killer

First recorded in 1525–35; kill ¹ + -er ¹

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Example Sentences

See Examples For:

killer killers

“As a lawyer, the procedural steps are absolutely critical to ensure that they get this right,” she told Fox News in an Aug. 31 appearance regarding the trial of Charlie Kirk’s accused killer.

From The Wall Street Journal ● Oct. 15, 2026

The jail, which opened in 1932 and has counted John Lennon's killer Mark David Chapman, rapper Tupac Shakur, and Sex Pistols musician Sid Vicious among its residents, was due to shutter by 2027.

From Barron's ● Oct. 12, 2026

Natural killer cells help regulate inflammation and the formation of new blood vessels through cytokine production and interactions with other immune cells.

From Science Daily ● Oct. 10, 2026

As OpenAI showed off its latest AI assistants in San Francisco last week, protesters outside — some dressed as killer robots —demanded it keep AI away from the military.

From Los Angeles Times ● Oct. 8, 2026

Sam pushes the stick shift into gear, and the vehicle lurches forward, weed killer sloshing in the giant tanks behind us.

From "Free Lunch" by Rex Ogle

Justice Secretary Alex Norris is expected to make a statement in Parliament early next week, announcing how the government will ensure the killers of PC Andrew Harper are not released early.

From BBC ● Aug. 29, 2026

He blended into the crowd, grew his beard, attended the mosques where the killers preached, listened, questioned, checked rumors.

From The Wall Street Journal ● Aug. 27, 2026

Some suggested these cells were relatively weak killers and could even suppress immune activity, while others found that they were highly effective at destroying target cells.

From Science Daily ● Aug. 25, 2026

But prolonged exposure produced cells that were poor killers.

From Science Daily ● Aug. 25, 2026

He had passed the point of no return: He had given aid and comfort to Abraham Lincoln’s killers and now he lied about it to protect them.

From "Chasing Lincoln's Killer" by James L. Swanson

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