killer

killer — noun

1. a person who takes another person's life, whether on purpose, by accident, or as

1.nounB1
Definition

a person who takes another person's life, whether on purpose, by accident, or as part of a crime

Example

The police arrested the **killer** outside his apartment building before dawn.

article + killer as a known referent

Hyun's family hoped the **killer** would be found and brought to court.

Common collocations
  • serial killer
  • cold-blooded killer
  • contract killer
  • spree killer
  • would-be killer
Synonyms
  • murderer

    specifically someone who kills on purpose and illegally; narrower than killer

  • assassin

    someone who kills for political reasons or payment; implies planning

  • slayer

    literary or dramatic; common in fantasy and mythology contexts

Antonyms
  • victim

    the person who is killed

Grammar Patterns

killer + of + person

Usage Note

Often modified by an adjective that specifies motive or method, such as serial killer, contract killer, or cold-blooded killer.

Common Mistakes

The murderer was found not guilty because he acted in self-defense.
The killer was found not guilty because he acted in self-defense.
murderer always implies unlawful intent; killer is neutral about legal guilt.

2. a disease or health condition that causes people to die, especially when many pe

2.nounB1
Definition

a disease or health condition that causes people to die, especially when many people are affected

Example

Heart disease is still the number one **killer** of women in the United States.

collocation: number one killer / biggest killer

Doctors called the virus a silent **killer** because victims showed no signs at first.

collocation: silent killer (disease without early symptoms)

Common collocations
  • number one killer
  • biggest killer
  • silent killer
  • top killer
Synonyms
  • epidemic

    focuses on rapid spread across a population, not necessarily the deadliness

  • plague

    historical and dramatic; a deadly disease that spreads very fast

Grammar Patterns

the + (number one / biggest) + killer + of + people / group

Usage Note

Commonly modified by number one, biggest, or silent to describe how widespread or undetectable the disease is.

3. a chemical, product, or substance made to destroy unwanted plants, insects, or o

3.nounB2
Definition

a chemical, product, or substance made to destroy unwanted plants, insects, or other harmful organisms

Example

Tanvi sprayed weed **killer** along the fence to stop the ivy from spreading.

compound noun: weed killer / pest killer

This ant **killer** comes in powder form and works best near doorways.

Common collocations
  • weed killer
  • pest killer
  • bug killer
  • ant killer
  • mould killer
Synonyms
  • pesticide

    more technical; covers all substances that kill pests, including insects and fungi

  • herbicide

    specifically for killing unwanted plants, not insects or bacteria

Grammar Patterns

[noun] + killer

killer + for + [target]

Usage Note

Usually appears as part of a compound noun (weed killer, pest killer, bug killer) rather than as a standalone word.

4. anything that completely ruins a relationship, activity, plan, or positive exper

4.nounB2
Definition

anything that completely ruins a relationship, activity, plan, or positive experience

Example

Money problems can be a real **killer** in a marriage if left unspoken.

collocation: real killer / relationship killer

A sudden power cut was a **killer** for the outdoor concert that night.

Common collocations
  • relationship killer
  • deal killer
  • mood killer
  • real killer
  • biggest killer
Synonyms
  • deal-breaker

    specifically in negotiations or relationships; something that makes an agreement impossible

Grammar Patterns

a / the + [adjective] + killer + of + [abstract noun]

Usage Note

Almost always used with a preceding modifier such as real, biggest, absolute, or a noun like relationship, deal, or mood.

5. a task, problem, or situation that demands an exhausting amount of effort to get

5.nounB2
Definition

a task, problem, or situation that demands an exhausting amount of effort to get through or solve

Example

The final exam was a real **killer** — most students ran out of time.

collocation: a real killer (informal for something very hard)

That mountain trail is a **killer** for beginners because of its steep climb.

Common collocations
  • real killer
  • absolute killer
  • a killer
Synonyms
  • nightmare

    stronger emotional tone; suggests stress and frustration more than pure difficulty

  • ordeal

    more formal; a long and painful experience

Antonyms
  • breeze

    something very easy to do — opposite in difficulty

  • cakewalk

    informal; something that requires almost no effort

Grammar Patterns

a real / absolute killer

Usage Note

Highly informal; common in spoken English. Avoid in formal writing — use challenge, ordeal, or demanding task instead.

Common Mistakes

The mathematics exam was a killer difficulty.
The mathematics exam was a killer.
killer already means 'very difficult thing'; do not add a second difficulty noun.

6. an exceptionally impressive or enjoyable person, story, show, or creative work t

6.nounC1
Definition

an exceptionally impressive or enjoyable person, story, show, or creative work that makes a strong impact on its audience

Example

Camila's new song is an absolute **killer** — I have listened to it ten times already.

collocation: absolute killer (extreme compliment)

That comedian's show was a **killer** from the first joke to the last encore.

Common collocations
  • absolute killer
  • real killer
Synonyms
  • hit

    popular and successful, but less intense than killer

  • showstopper

    a performance so good it gets interrupted by applause

Antonyms
  • flop

    a performance or product that fails completely

Grammar Patterns

a(n) + [intensifier] + killer

Usage Note

Always positive and enthusiastic. Less common than the 'difficult' sense; context (entertainment, sports, conversation) makes the meaning clear.

killer — adjective

Word family

  • kill
    verbA2
  • killing
    nounB2
  • killing
    adjectiveC1

Synonym discussion

Sense: noun/1

All four words describe someone who takes another person's life, but they differ in legal status, motive, and register. Killer is the most neutral and general term — it covers anyone who causes a death, whether by accident, in self-defense, or as a crime. A driver who hits a pedestrian is a killer but not a murderer. Murderer is narrower and carries legal weight: it means someone who killed on purpose and illegally. You would not call a soldier at war a murderer unless the killing violated the laws of war. Assassin implies planning, a target, and a motive that is usually political or financial — a contract killer is a type of assassin, but a jealous spouse who kills is not. Slayer belongs to a more dramatic or literary register, common in fantasy stories ('the dragon slayer') and news headlines for dramatic effect. In everyday conversation, killer is by far the most frequent, while the others add specific connotations of intent, method, or tone.

murdererassassinslayer

Common collocations

Phrases

  • a real killer
  • an absolute killer
  • the number one killer
  • the biggest killer

Prepositions

  • killer of

Etymology

Old EnglishMiddle EnglishEnglish

Killer comes from the verb kill, which traces back to the Old English word cwellan, meaning 'to die' or 'to cause to die.' The noun killer (someone who kills) appeared in the 1400s. The informal adjective use meaning 'extremely impressive' emerged in American English slang during the 1970s, originally in African American and jazz subcultures, then spread to mainstream speech.