English Reference
noun · adjective

killer

n. · adj.
US /ˈkɪɫɝ/ UK /kˈɪlɐ/ killer UK spelling killers

  1. 01 A2 Elementary

    n.a person, animal, or thing that causes death.

    n.a person, animal, or agent that causes the death of another living being.

    Simple

    The police are still searching for the killer after the attack.

    In context

    The documentary explores how the invasive species became a silent killer of the local bird population within just a few years.

  2. 02 B2 Upper Intermediate Informal

    n.something that is extremely hard to do or causes a lot of stress.

    n.a task, situation, or experience that is exceptionally taxing or difficult to endure.

    Simple

    That three-hour exam was a real killer.

    In context

    The final climb of the race is a absolute killer, forcing even the most seasoned cyclists to push their physical limits.

    breezecinch
  3. 03 B1 Intermediate Science

    n.another name for an orca.

    n.a common shorthand for the orca (Orcinus orca).

    Simple

    We saw a pod of killer whales swimming near the boat.

    In context

    Marine biologists observed the killer whales using sophisticated hunting techniques to isolate their prey from the rest of the pod.

    orca
  4. 04 B2 Upper Intermediate Slang

    adj.very impressive, effective, or cool.

    adj.strikingly effective, impressive, or fashionable. Often used in marketing or casual praise.

    Simple

    She gave a killer presentation that convinced the whole board.

    In context

    The startup's new app features a killer interface that sets it apart from every other competitor in the crowded fintech market.

  5. 05 B2 Upper Intermediate

    adj.deadly or very dangerous.

    adj.having the capacity or tendency to cause death or total destruction.

    Simple

    The city was hit by a killer heatwave last summer.

    In context

    The researchers identified a killer strain of the virus that appeared resistant to conventional antibiotic treatments.

Usage killer back

Heat is the leading weather-related killer in the United States.

Ars Technica· 18 Aug 2026

Government sources confirmed on Monday night that officials were still examining whether they could block the release of Harper’s killers.

The Guardian· 11 Aug 2026

From Middle English killer, kyller. By surface analysis, kill + -er.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Origin Middle English killer
Level B2 · Upper Intermediate
Frequency Common
Updated