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Synonyms

deadly

American  
[ded-lee] / ˈdɛd li /

adjective

deadlier, deadliest
  1. causing or tending to cause death; fatal; lethal.

    a deadly poison.

  2. aiming to kill or destroy; implacable.

    a deadly enemy.

  3. like death.

    a deadly pallor.

  4. excruciatingly boring.

    The dinner party was absolutely deadly.

    Synonyms:
    dreary, tedious, dull
  5. excessive; inordinate.

    deadly haste.

  6. extremely accurate.

    Annie Oakley was a deadly shot.


adverb

  1. in a manner resembling or suggesting death.

    deadly pale.

  2. excessively; completely.

    deadly dull.

deadly British  
/ ˈdɛdlɪ /

adjective

  1. likely to cause death

    deadly poison

    deadly combat

  2. informal extremely boring

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

adverb

  1. like death in appearance or certainty

    deadly pale

    a deadly sleep

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Related Words

See fatal.

Other Word Forms

  • deadliness noun
  • nondeadly adjective

Etymology

Origin of deadly

First recorded before 900; Middle English deedli(ch), Old English dēadlīce; dead, -ly

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Only a Mars landing ranks lower, while monitoring for deadly asteroids and measuring climate change are top priorities among Americans.

From Salon • Apr. 7, 2026

Air India's chief executive officer Campbell Wilson has resigned as the airline deals with challenges, including financial losses and the aftermath of a deadly crash last year that killed 260 people.

From BBC • Apr. 7, 2026

Damburger survived the deadly 2018 Carr fire that took out a swath of west Redding, burning within two miles of the restaurant.

From Los Angeles Times • Apr. 7, 2026

Keenan played a similar role in the civil-rights prosecutions of Louisville, Ky., police officers involved in the deadly 2020 raid on Breonna Taylor’s home.

From The Wall Street Journal • Apr. 7, 2026

Carriage accidents were serious in wartime Washington and could prove deadly.

From "Chasing Lincoln's Killer" by James L. Swanson