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

In response to legislation to end the cruelty once and for all, the Daily News once again trotted out its old and tired defense of this cruel, deadly and outdated industry. — Voice Of The People, New York Daily News, 18 Oct. 2026 The Houthis have targeted Saudi oil tankers transiting the Bab al-Mandeb Strait and, in recent days, launched deadly strikes on Riyadh’s main international airport. — Lou Robinson, CNN Money, 17 Oct. 2026

Adverb

MacDonald and editor Phil Hignett have a keen, witty sense of how the online realm crashes offline living, seamlessly integrating deadly-accurate TikTok parodies into the film’s breezy narrative flow. — Guy Lodge, Variety, 26 Aug. 2026 The disagreement leaves the government to determine when one of the world’s largest apparel-exporting industries must reopen a wage debate that turned deadly less than three years ago. — Alexandra Harrell, Footwear News, 24 Aug. 2026 See All Example Sentences for deadly

Recent Examples of Synonyms for deadly

Adjective

Just two days earlier, Florida executed James Robertson by lethal injection at the same prison.

— Richard Nichols, The Orlando Sentinel, 18 Oct. 2026
Prison staff gave Pike two doses of pentobarbital, the drug used for lethal injections.

— Arkansas Online, Arkansas Online, 16 Oct. 2026

Definition of lethal

Adjective

Airing for eight seasons between 1964 and 1972, the fantastical series followed the daily adventures of a powerful witch who attempted to live as a typical suburban housewife alongside her mortal husband.

— Justine Fisher, PEOPLE, 12 Oct. 2026
Waymo’s sales pitch is that its technology will remove all that mortal imperfection from our streets.

— Molly Fischer, New Yorker, 12 Oct. 2026

Definition of mortal

Adverb

Some wondered whether Schrödinger’s equation might be an approximation that works extremely well at the microscopic scale but breaks down at the macroscopic scale, which would mean the measurement postulate of the Copenhagen interpretation is right.

— Philipp Strasberg, Scientific American, 20 Oct. 2026
In the meantime, no one should refrain from using sunscreen, which is extremely well-proven to cause cancer.

— Tracy Middleton, Allure, 19 Oct. 2026

Definition of extremely

Adjective

Another e-bike rider died over the weekend in Huntington Beach, marking the second fatal incident involving an e-bike in the coastal city in months.

— Summer Lin, Los Angeles Times, 19 Oct. 2026
Presley, Crawford’s son and Kaia’s older brother, died of a fatal overdose inside a rehab facility after years of struggling with addiction and his mental health.

— Jason P. Frank, Vulture, 19 Oct. 2026

Definition of fatal

Adjective

In 2024, Michigan State launched Rx Kids, the country’s first universal and unconditional prenatal and infant cash program.

— Mona Hanna, Washington Post, 8 Oct. 2026
Once a seller has an unconditional right to receive the proceeds, many planning opportunities may no longer be available.

— D. Scott Kenik, Forbes.com, 2 Oct. 2026

Definition of unconditional

Adjective

Two men were found dead inside a Long Beach home after one of them exchanged shots with police and sparked a standoff with SWAT officers in a residential neighborhood early Saturday morning, police said.

— Los Angeles Times, Los Angeles Times, 18 Oct. 2026
The film follows a Polish burglar who assumes the identity of a dead stranger’s girlfriend, with unexpected results.

— Georg Szalai, HollywoodReporter, 18 Oct. 2026

Definition of dead

Adverb

While these issues can be addressed, the costs can be incredibly high, and under Florida law, developers are only on the hook for anything identified within the first seven years after a building is handed over to the homeowners association.

— Denise Hruby, Miami Herald, 19 Oct. 2026
The pre-selection debates about three- or four-loss SEC squads and some team no one actually watches will prove incredibly tiresome, too.

— Tyler Estep, AJC.com, 19 Oct. 2026

Definition of incredibly

Cite this Entry

Style

“Deadly.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/deadly. Accessed 21 Oct. 2026.

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