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

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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

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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

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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

Switzerland’s deadliest mass shooting occurred in 2001, when a gunman killed 14 politicians in what became known as the Zug massacre. — Sophie Tanno, CNN Money, 30 Aug. 2026 Candida auris can live on surfaces in healthcare facilities and cause deadly infections in humans. — Katia Riddle, NPR, 29 Aug. 2026

Adverb

What makes the Andes virus so deadly? — Lauren Dunn, NBC news, 7 May 2026 Fentanyl is a deadly synthetic opioid. — Rosalio Ahumada, Sacbee.com, 6 May 2026 See All Example Sentences for deadly

Recent Examples of Synonyms for deadly

Adjective

Dozens of companies have withdrawn over the past decades due to poor profits, an uncertain business outlook and concerns about harm to their reputations from making arms, especially lethal weapons.

— Mia Osmonbekov, Fortune, 31 Aug. 2026
Airwars is the first to map the damage radius of the strikes in Lamerd and estimate the lethal range of the weapon used.

— Julia Frankel, Los Angeles Times, 31 Aug. 2026

Definition of lethal

Adjective

The facts of his biography, no matter how outrageous, could not possibly explain the sheer derangement of his output.

— Becca Rothfeld, New Yorker, 29 Aug. 2026
This means investor scrutiny will extend beyond the sheer scale of AI investment to encompass debt burdens, capital costs, and return timelines.

— , CNBC, 28 Aug. 2026

Definition of sheer

Adjective

Joseph lauded Walsh’s steadiness in the face of mortal danger and noted that Walsh, after being shot twice in the torso and returning fire that killed the suspect, walked out of the house on his own power and called for his own ambulance.

— Robert Salonga, Mercury News, 26 Aug. 2026
By suggesting that Black women would willingly place their own children in mortal danger for profit, such narratives provided yet another means of humiliating, degrading and dehumanizing African Americans.

— The Conversation, The Conversation, 11 Aug. 2026

Definition of mortal

Adverb

This pre-seasoned, ¼ inch thick steel heat extremely evenly with minimal disparity between the center and edges.

— Adam Campbell-Schmitt, Bon Appetit Magazine, 31 Aug. 2026
Search for jet quenching Previous experiments suggest that a millionth of a second after the Big Bang, even as temperatures remained extremely high, matter did not behave like gas but instead like liquid with very low viscosity.

— Ameya Paleja, Interesting Engineering, 31 Aug. 2026

Definition of extremely

Adjective

An incident that for others might be fatal—a free fall from a high bridge—affects the coyote for only a brief moment.

— Zach Helfand, New Yorker, 31 Aug. 2026
There is a broad debate over the applicability of PNB to modern anti-trust cases, with many legal scholars finding the application of a random number, without any real analysis of the potential harm a merger might cause, to be a fatal flaw.

— Shubha Ghosh, Fortune, 31 Aug. 2026

Definition of fatal

Adjective

The capitulation of Germany is at hand, the Third Reich's unconditional surrender just days away.

— Danielle Parker, CBS News, 28 Aug. 2026
Despite his resolve to be gentler and kinder than Cotton, Hank still struggles to articulate his unconditional love to his son, Bobby.

— Jordana Rosenfeld, Encyclopedia Britannica, 24 Aug. 2026

Definition of unconditional

Adjective

Current policy allows airport facilities to be named only for people who have been dead at least two years and who made significant contributions to the airport authority or aviation in Middle Tennessee.

— Hadley Hitson, USA Today, 28 Aug. 2026
To that end, Chris Diamantopoulos looks like an inspired bit of casting as Mitch McNamara, a government agent who swoops in to examine eight dead Jasons and a ninth the police are holding in an interrogation room.

— Scott Tobias, Vulture, 28 Aug. 2026

Definition of dead

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“Deadly.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/deadly. Accessed 1 Sep. 2026.

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