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

Once again, he said, the state was trying to rip away his good name and falsely brand him a killer.

From Salon ● Aug. 10, 2026

A new documentary on the 2022 slayings of four University of Idaho students highlights the lives of the victims instead of feeding grim fascination with the killer.

From The Wall Street Journal ● Jul. 29, 2026

She may be a killer, but she isn’t the villain.

From Los Angeles Times ● Jul. 27, 2026

Now, as the trial of Tyler Robinson, Kirk’s alleged killer, begins, something has replaced that reverence.

From Slate ● Jul. 27, 2026

But the historical record makes Homo sapiens look like an ecological serial killer.

From "Sapiens: A Brief History of Humankind" by Yuval Noah Harari

Former police dog handler Chris Bushnell, who was at the scene of PC Harper's death, said he was "shaking" when he heard that two of the officer's killers might be released early from prison.

From BBC ● Aug. 11, 2026

She added she was not looking for a "special case" for her son, but wanted the killers of all emergency workers to be exempt from the early release scheme.

From BBC ● Aug. 11, 2026

Last week, PC Harper's widow, Lissie Harper, said she "will not give up" and hoped people would share a petition calling for his killers to be denied early release from prison.

From BBC ● Aug. 11, 2026

The move comes after days of pressure to exclude Harper's killers from the scheme, which is aiming to free about 5,000 offenders in England and Wales to make space in overcrowded jails.

From BBC ● Aug. 11, 2026

Most serial killers are animal lovers, I read that once.

From "I'll Give You the Sun" by Jandy Nelson