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

Fentanyl, which is 50 to 100 times more potent than heroin, is now giving way to even deadlier compounds such as the 10-times more powerful cychlorphine. —

The Week Us, TheWeek, 18 May 2026 The report is the final analysis by the Global Preparedness Monitoring Board, a World Health Organization (WHO) group established in the wake of West Africa’s 2016 Ebola epidemic to assess how well countries were prepared to face a deadly pandemic. —

Claire Cameron, Scientific American, 18 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

Prosecutors also displayed the internet search history from Richins’ phone, which included queries about the lethal dose of fentanyl, luxury prisons and how poisoning is marked on a death certificate.

— Hannah Schoenbaum, Chicago Tribune, 13 May 2026
In a letter last month, the federal Substance Abuse and Mental Health Services Administration notified federal grant recipients that the government would no longer pay for test strips and kits that help drug users see if their drugs contain highly-lethal additives.

— Mike Stobbe, Fortune, 13 May 2026