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

Related Stories The finale starts off with a flashback to Sheriff Kerry Kane (Kelly Macdonald) picking up Jordan from prison following a 10-year sentence after admitting fault for the deadly attack on Rushfield. — Justin Kroll, Deadline, 4 Oct. 2026 All three victims of the deadly medical helicopter crash off Catalina Island have been publicly identified. — Iris Kwok, Los Angeles Times, 3 Oct. 2026

Adverb

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 Police are investigating a double shooting that turned deadly early Sunday morning in North Philadelphia. — Laura Fay, CBS News, 9 Aug. 2026 See All Example Sentences for deadly

Recent Examples of Synonyms for deadly

Adjective

As the most lethal and airborne variant of the infection, pneumonic plague is nearly always fatal unless specific antibiotics are given quickly.

— Mrigakshi Dixit, Interesting Engineering, 5 Oct. 2026
Graham had four pressures as a blitzer and has looked absolutely lethal in that role.

— Ryan Kartje, Los Angeles Times, 5 Oct. 2026

Definition of lethal

Adjective

Known as the Shark Bay UNESCO World Heritage Site, the place gets its name from English buccaneer-cum-naturalist William Dampier, who was overcome by the bay’s sheer abundance and the size of the marine predators during a visit in 1699.

— Literary Hub, Literary Hub, 2 Oct. 2026
Through the sheer force of his will and his brilliant comedic timing, Bratton was elevated to a cast member by the second season.

— Andy Greene, Rolling Stone, 2 Oct. 2026

Definition of sheer

Adverb

Eco effort D’Inghilterra’s sustainability efforts stand out at Café Romano where the ingredients are local and extremely fresh—the chef likely selected the veggies in your salad from the market that morning.

— Condé Nast, Condé Nast Traveler, 6 Oct. 2026
Arrests near schools or colleges have increased, though enforcement actions on campuses are extremely uncommon.

— Mathew Miranda, Sacbee.com, 6 Oct. 2026

Definition of extremely

Adjective

Independent media outlets like Baikal People reported that the fatal chain of events began on September 25.

— Mrigakshi Dixit, Interesting Engineering, 5 Oct. 2026
Chicago Alderman Michelle Harris said at Sunday's community vigil that the suspect had allegedly gotten into an altercation with staff at a wireless store in the Chatham neighborhood just before the fatal stabbing, WLS reported.

— ABC News, ABC News, 5 Oct. 2026

Definition of fatal

Adjective

South Korea has not given the project an unconditional green light and says its participation will depend on the economics.

— Neetika Walter, Interesting Engineering, 30 Sep. 2026
Kremlin spokesman Dmitry Peskov repeated Moscow's demand for a comprehensive peace deal, not a temporary break in hostilities, following Ukraine's call for a complete and unconditional ceasefire.

— HANNA ARHIROVA, Arkansas Online, 25 Sep. 2026

Definition of unconditional

Adjective

To assist Noah, Sinestro has also forged a new lantern from the water on this dead alien planet — imbued with Zoe’s fear toxins — causing golden cracks in the object’s surface.

— Siddhant Adlakha, Vulture, 5 Oct. 2026
Urker, who also fathered a baby girl, Aurora, with Blanchard, was found dead Thursday in Raceland, Louisiana.

— Payton Turkeltaub, Variety, 4 Oct. 2026

Definition of dead

Adverb

The rooms are incredibly cozy, with gas fireplaces, a pull-out couch, and framed images of different landmarks around the Presidio.

— Condé Nast, Condé Nast Traveler, 6 Oct. 2026
His incredibly sharp eye for talent coupled with strong instincts and deep relationships are a dynamic combination for artist management.

— Matt Grobar, Deadline, 5 Oct. 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 9 Oct. 2026.

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