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

Having a killer cover letter used to be the way to stand out from other applicants with similar resumes.

From MarketWatch ● Jul. 15, 2026

He’s not Jeff Goldblum-level rascally, but he’s confident enough to go his own way and make a killer joke at a high-voltage fence.

From Los Angeles Times ● Jul. 13, 2026

The famous Buddhist Angulimala Sutta tells a story of a serial killer who is redeemed by the Buddha and becomes a righteous monk.

From Slate ● Jul. 10, 2026

The shower, I explain to my friends for the 15th time, is a silent killer.

From The Wall Street Journal ● Jul. 9, 2026

A killer whale surfaced beside the ship, its black sides glistening and its white patches tinged a dirty yellow by algae.

From "Shipwreck at the Bottom of the World" by Jennifer Armstrong

Diaz’s attorney, Matthew Barhoma, also maintained that his client is innocent — and blamed ICE for letting the people he accused of being the real killers get away with it.

From Los Angeles Times ● Jul. 8, 2026

They're terrific footballers, very easy on the eye, but they're not ruthless, not killers.

From BBC ● Jun. 20, 2026

It is increasingly understood as a quiet, common, and dangerous disorder that can be detected earlier, treated sooner, and linked closely to some of the world's biggest killers.

From Science Daily ● May 29, 2026

Ford, who escaped two would-be killers in less than one month, only narrowly lost the 1976 election despite running in the shadow of Watergate.

From Slate ● Apr. 26, 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