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

Relevance

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

When the Guadalupe River surged through Texas Hill Country last summer, Elida Sierra Lutz and her three children were swept into the deadly flooding like debris in the current. — Alisha Ebrahimji, CNN Money, 6 July 2026 In 2025, Djokovic had the fourth-highest percentage of service games won, placed between Reilly Opelka and Giovanni Mpetshi Perricard, two of the game’s most deadly servers. — Charlie Eccleshare, New York Times, 5 July 2026

Adverb

This was a black one with blotches faintly outlined in pale yellow, a beautiful but deadly looking animal. — Dr. C. E. Kuschel, Outdoor Life, 9 Apr. 2026 While the victim usually endures just a bit of dampness, police said the game can look deadly serious for people who may be witnessing it. — Clifford Ward, Chicago Tribune, 10 Apr. 2026 See All Example Sentences for deadly

Recent Examples of Synonyms for deadly

Adjective

The theory is that individuals became infected by a strain that was particularly lethal to the young through close contact with marmots (rodents that are known reservoirs of the plague), perhaps while butchering them.

— The Week UK, TheWeek, 6 July 2026
Hubris and risk aversion make for a lethal cocktail in high-level professional sports.

— Dieter Kurtenbach, Mercury News, 6 July 2026

Definition of lethal

Adjective

The sleeveless gown featured a semi-sheer corset bodice with a curtain of lace foliage that cascaded down past the thigh-high slit, forming an elegant silhouette.

— Chanel Vargas, InStyle, 5 July 2026
Nonetheless, some 120,000 Mint Juleps are consumed across two sunny days at Churchill Downs during the Kentucky Derby, proving that some cocktails can become refreshing daytime summer sippers just by sheer force of will, and a little crushed ice.

— Jeremy Repanich, Robb Report, 4 July 2026

Definition of sheer

Adverb

The team turned to the Advanced Photon Source at Argonne National Laboratory, a stadium-sized synchrotron facility that produces extremely bright X-ray beams.

— New Atlas, New Atlas, 6 July 2026
Teasing out the impact of a small dose of radiation that occurs in addition to all those other exposures is extremely challenging, and the impact of extremely low exposures has not been decisively demonstrated.

— ArsTechnica, ArsTechnica, 6 July 2026

Definition of extremely

Adjective

Although most people recover from Legionnaires' disease with antibiotics, certain patients -- including those who are immunocompromised or who suffer from chronic lung diseases -- can develop complications that can be fatal.

— Mary Kekatos, ABC News, 7 July 2026
The Grand Prairie Police Department is investigating a fatal crash in which a passenger vehicle hit a pedestrian.

— Mary Ella Hastings July 6, Fort Worth Star-Telegram, 7 July 2026

Definition of fatal

Adjective

Ramp, the corporate card and expense management company backed by Iconiq and valued at $44 billion, is now Senra’s largest advertiser and, by CEO Glyman’s own description, an unconditional backer.

— Lily Mae Lazarus, Fortune, 5 July 2026
At its deepest level, this work is fueled by unconditional love—not sentimental or passive love but love as discipline, courage and commitment.

— Yujia Zhu, Forbes.com, 2 July 2026

Definition of unconditional

Adjective

There were no signs of rodents at any businesses during this inspection period, but dead roaches were found at Conservatory at Plano, at 6401 Ohio Drive.

— Mary Ella Hastings July 3, Fort Worth Star-Telegram, 4 July 2026
She was flown by Life Flight to a local hospital, where she was later pronounced dead.

— Michael Sinkewicz, FOXNews.com, 3 July 2026

Definition of dead

Cite this Entry

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“Deadly.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/deadly. Accessed 7 Jul. 2026.

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Synonyms of deadly

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adverb

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