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

Etymology

Origin of killer

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

Example Sentences

See Examples For:

killer killers

Slasher movies have always depended on a memorable killer, and the genre has produced some of horror’s most instantly recognizable figures.

From Los Angeles Times ● Sep. 25, 2026

Diesel’s recent price jump is “kind of a silent killer to people’s wallets,” said Denton Cinquegrana, chief oil analyst at Dow Jones Energy.

From MarketWatch ● Sep. 23, 2026

You might remember Pamela as the killer in the original film—a trivia fact horror fans love to share.

From The Wall Street Journal ● Sep. 19, 2026

Police have said they are not sure if they are hunting a serial killer.

From BBC ● Sep. 18, 2026

But if I went through with the exorcism, I would be severing my only lead to finding Yakov’s true killer.

From "The City Beautiful" by Aden Polydoros

She has now ordered an independent review into what happened and said she understood why it would be distressing for Karol Kelly's family that one of his killers remains on the run.

From BBC ● Sep. 22, 2026

Prime Minister Andy Burnham has told the BBC that PC Andrew Harper's killers will remain behind bars as he announced changes to the early release scheme aimed at easing prison overcrowding.

From BBC ● Aug. 30, 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

But prolonged exposure produced cells that were poor killers.

From Science Daily ● Aug. 25, 2026

Unfortunately, a good many chemicals also have the power to separate oxidation from energy production, and the insecticides and weed killers are well represented on the list.

From "Silent Spring" by Rachel Carson