DEADLY Synonyms: 324 Similar and Opposite Words

Q: How does the adjective 'deadly' differ from other similar words?

Some common synonyms of deadly are fatal , lethal , and mortal . While all these words mean "causing or capable of causing death," deadly applies to an established or very likely cause of death. // a deadly disease

Q: When would 'fatal' be a good substitute for 'deadly'?

In some situations, the words fatal and deadly are roughly equivalent. However, fatal stresses the inevitability of what has in fact resulted in death or destruction. // fatal consequences

Q: When is 'lethal' a more appropriate choice than 'deadly'?

While in some cases nearly identical to deadly , lethal applies to something that is bound to cause death or exists for the destruction of life. // lethal gas

Q: When could 'mortal' be used to replace 'deadly'?

The synonyms mortal and deadly are sometimes interchangeable, but mortal implies that death has occurred or is inevitable. // a mortal wound

deadly 1 of 2

adjective

ˈded-lē

Definition of deadly

as in lethal

likely to cause or capable of causing death the doctors were alarmed about the outbreak of the deadly new virus

Synonyms & Similar Words

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Antonyms & Near Antonyms

as in sheer

having no exceptions or restrictions the deadly tedium of waiting for the fog to lift

Synonyms & Similar Words

Antonyms & Near Antonyms

as in mortal

of, relating to, or suggestive of death a deadly pallor spread across her face as the tragic news gradually sank in

Synonyms & Similar Words

Antonyms & Near Antonyms

deadly

2 of 2

adverb

as in extremely

to a great degree I'm deadly serious about making an offer on the house

Synonyms & Similar Words

Antonyms & Near Antonyms

Synonym Chooser

How does the adjective deadly differ from other similar words?

Some common synonyms of deadly are fatal, lethal, and mortal. While all these words mean "causing or capable of causing death," deadly applies to an established or very likely cause of death.

a deadly disease

When would fatal be a good substitute for deadly?

In some situations, the words fatal and deadly are roughly equivalent. However, fatal stresses the inevitability of what has in fact resulted in death or destruction.

fatal consequences

When is lethal a more appropriate choice than deadly?

While in some cases nearly identical to deadly, lethal applies to something that is bound to cause death or exists for the destruction of life.

lethal gas

When could mortal be used to replace deadly?

The synonyms mortal and deadly are sometimes interchangeable, but mortal implies that death has occurred or is inevitable.

a mortal wound

Example Sentences

Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.

Recent Examples of deadly

Adjective

The danger carried grim resonance in a region where the 2018 Mati wildfire killed 104 people, Europe’s deadliest blaze this century. — Elena Becatoros, Los Angeles Times, 2 Aug. 2026 That's because breastmilk helps build a baby's immunity against potentially deadly diseases. — Diaa Hadid, NPR, 2 Aug. 2026

Adverb

Like those albums, LP4 operates with its own sense of logic and time, sounding alternately playful and deadly serious, proudly complex and refreshingly pared back. — Sam Sodomsky, Pitchfork, 4 May 2026 In Langbein’s comic, but also deadly serious, imagination, this is no mere metaphor. — Los Angeles Times, 22 Apr. 2026 See All Example Sentences for deadly

Recent Examples of Synonyms for deadly

Adjective

The scheduling of two executions – both via lethal injection – in one day comes as Florida has accelerated its pace of executions, even as other states have abolished or paused the practice.

— Nicki Brown, CNN Money, 26 July 2026
Filing murder charges against people who provide lethal doses of fentanyl is relatively new in California.

— Clara Harter, Los Angeles Times, 25 July 2026

Definition of lethal

Adjective

Cyrus’ flawless-looking skin was in part thanks to the Maybelline New York Lifter Plump and Glow Foundation, a sheer base that can be built up for more coverage.

— Clara McMahon, PEOPLE, 1 Aug. 2026
For her main ensemble, the Catwoman star wore head-to-toe black, including a strappy triangle bikini layered beneath a semi-sheer coverup that doubled as a minidress.

— Chanel Vargas, InStyle, 1 Aug. 2026

Definition of sheer

Adverb

Analyzing top player movement Changing schools is extremely common, with more than 17,000 athletes in Texas filling out a prior athletic participation form (PAPF) this past year, according to UIL executive director Jamie Harrison.

— Charles Baggarly, Fort Worth Star-Telegram, 28 July 2026
Here’s an outpost of a chain with some extremely personal, local touches.

— Condé Nast, Condé Nast Traveler, 28 July 2026

Definition of extremely

Adjective

Legal experts cast doubt Monday on Bryan Kohberger’s petition to withdraw his guilty plea in the fatal stabbings of four University of Idaho students in 2022.

— Emanuella Grinberg, NBC news, 28 July 2026
Tasmanian devils suffer from Devil Facial Tumor Disease (DFTD), a highly fatal cancer spread by biting, which has devastated their population and surprisingly arose twice.

— John Drake, Forbes.com, 27 July 2026

Definition of fatal

Adjective

My love is unconditional and nothing will separate me from your cheesy beefy burrito and avocado chicken stacker.

— Teresa Mull, FOXNews.com, 31 July 2026
Each fellow will also retain the unconditional right to publish in any journal, even if the findings are critical of Polymarket.

— Camila Grigera Naón, Fortune, 29 July 2026

Definition of unconditional

Adjective

Despite continued life-saving efforts by first responders, the girl was pronounced dead before she could be airlifted to a hospital.

— Richard Ramos, CBS News, 1 Aug. 2026
Investigators declared the driver of the white SUV, a 53-year-old man, dead at the scene, Moncayo said.

— Caroline Zimmerman, Kansas City Star, 1 Aug. 2026

Definition of dead

Adverb

This in addition to an incredibly massive health data and tracking software and app market, which has grown significantly since the early days of the smartphone.

— Forbes.com, Forbes.com, 28 July 2026
That’s only a 30% drop from its first weekend, an incredibly modest slide for a blockbuster.

— Lindsey Bahr, Fortune, 27 July 2026

Definition of incredibly

Cite this Entry

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“Deadly.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/deadly. Accessed 3 Aug. 2026.

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