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 next

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

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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

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

Launched overnight on Thursday to Friday, the drone salvo — one of Ukraine's deadliest such strikes in months — also wounded 42 in Starobilsk, in the occupied Lugansk region, trapping people beneath the debris. —

CBS News, 24 May 2026 Mosquitoes are considered the world’s deadliest animal, according to the Centers for Disease Control and Prevention. —

Janet Loehrke, USA Today, 24 May 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 Clooney was reacting playfully in his statement to Deadline but was deadly serious in his recent public comments. —

Mike Fleming Jr, Deadline, 8 Apr. 2026 See All Example Sentences for deadly

Recent Examples of Synonyms for deadly

Adjective

Many who lived through the pandemic—and witnessed this inability to combat the lethal pestilence—developed scornful opinions of the medical profession.

— Literary Hub, Literary Hub, 27 May 2026
The lethal nature of mosquitoes is ancient knowledge, encoded in some of our most sacred texts.

— Ross Andersen, The Atlantic, 27 May 2026