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

The deadly fungi are found in California, Oregon and Washington state. —

Sacbee.com, 1 June 2026 Melanoma is the deadliest form of skin cancer, and in about half of patients, the disease will come back within the first five years of treatment. —

Kaitlin Sullivan, NBC news, 1 June 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

Hurricane Andrew — the lethal 1992 storm that almost always gets invoked as a cautionary tale — struck during a relatively quiet year and though fierce, was puny by comparison.

— Miami Herald Archives, Miami Herald, 3 June 2026
Throughout the game, players can create distractions and temporarily scare off the dinosaurs using non-lethal weaponry.

— Payton Turkeltaub, Variety, 3 June 2026