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.

---

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

---

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

Could Tupac verdict inspire new efforts to find killer of his rival the Notorious B.I.G.?

From BBC ● Sep. 2, 2026

Forecasters last weekend had issued flash-flood warnings for the area and said certain spots “can become raging killer currents in a matter of minutes.”

From The Wall Street Journal ● Aug. 31, 2026

“She’s been nothing but professional and an absolute killer when it comes to getting her job done,” Luna said.

From Los Angeles Times ● Aug. 30, 2026

The key to a killer résumé is your perfect scrambled eggs.

From The Wall Street Journal ● Aug. 26, 2026

He knew everyone was focused on Ernie, but he was still a bird killer.

From "As Brave As You" by Jason Reynolds

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

More than 30 families have called on the government to stop killers convicted of any form of manslaughter being released early to ease prison overcrowding in England and Wales.

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

The principal recorded killers were smallpox, influenza, measles, typhoid, typhus, chicken pox, whooping cough, tuberculosis, and syphilis.

From "Guns, Germs, and Steel: The Fates of Human Societies" by Jared M. Diamond