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 Tip Toe, Manchester gay bar owner Leo Struthers (Alan Cumming) and electrician neighbor Clive Goss’ (David Morrissey) feud takes a deadly turn when online conspiracy theories and anti-LGBTQ rhetoric come into play. — Glenn Garner, Deadline, 4 July 2026 Lampedusa, which lies between Tunisia, Malta and Sicily, sits on one of the world’s deadliest migration routes. — Reuters, NBC news, 4 July 2026

Adverb

Like those albums, LP4 operates with its own sense of logic and time, sounding alternately playful and deadly serious, proudly complex and refreshingly pared back. — Sam Sodomsky, Pitchfork, 4 May 2026 In Langbein’s comic, but also deadly serious, imagination, this is no mere metaphor. — Los Angeles Times, 22 Apr. 2026 See All Example Sentences for deadly

Recent Examples of Synonyms for deadly

Adjective

The most common type is lethal in about half of patients, and death is almost instantaneous.

— Veronique Greenwood, Time, 13 July 2026
Tewalt previously cautioned state lawmakers that transitioning from lethal injection to a firing squad as Idaho’s preferred method would result in even more lawsuits.

— Kevin Fixler, Idaho Statesman, 10 July 2026

Definition of lethal

Adjective

The divisive trend first crossed my desk when Jennifer Lawrence stepped out in Paloma Wool’s sheer sarong-style version of the piece last summer, pairing the flowy garment with a cool oversized T-shirt and strappy sling-backs.

— Emily Tannenbaum, Glamour, 11 July 2026
Perfumers often create this effect with notes like white musk, skin musk, aldehydes, watery florals, sheer woods, and delicate citrus, which together can evoke a cozy sense of self-care.

— Christa Joanna Lee, Allure, 11 July 2026

Definition of sheer

Adjective

Early in this week’s episode of Cape Fear, Natalie Bowden has been sent away from the latest mortal threat to the Bowden family and asked to spend some time with Paul, the vaguely smarmy man that she’s long been told is her biological father.

— Scott Tobias, Vulture, 10 July 2026
In an interview, Worner said that while saints are ultimately mortal and therefore not perfect, there is a certain criterion of morality decided by a multitude of individuals.

— Vivian Wilson, Twin Cities, 8 July 2026

Definition of mortal

Adverb

Be vigilant about never leaving young children and pets in vehicles without supervision, especially during periods of intense heat, as car interiors can quickly become extremely hot.

— CA Weather Bot, Sacbee.com, 14 July 2026
Surveillance of a suspect can take hours or days, and is extremely resource-intensive.

— Caroll Alvarado, CNN Money, 14 July 2026

Definition of extremely

Adjective

Like many Maine officials, Biddeford mayor Liam LaFountain has called for a thorough and transparent investigation into the fatal shooting of 26-year-old Joan Sebastian Guerrero at the hands of a federal agent.

— Caroll Alvarado, CNN Money, 14 July 2026
In the third season, Juliette has lost her memories in the process of surviving a near-fatal experience being locked in an incinerator.

— Dessi Gomez, Deadline, 13 July 2026

Definition of fatal

Adjective

Ramp, the corporate card and expense management company backed by Iconiq and valued at $44 billion, is now Senra’s largest advertiser and, by CEO Glyman’s own description, an unconditional backer.

— Lily Mae Lazarus, Fortune, 5 July 2026
At its deepest level, this work is fueled by unconditional love—not sentimental or passive love but love as discipline, courage and commitment.

— Yujia Zhu, Forbes.com, 2 July 2026

Definition of unconditional

Adjective

Inside, a man and woman believed to be in their mid-40s were found dead from gunshot wounds.

— Clara Harter, Los Angeles Times, 11 July 2026
In a subsequent lecture, Halford noted that snake venom’s effect on the blood was like that of cholera, and modestly suggested that the venom of dead snakes, dried and carried aloft on the wind, might be the cause of that disease.

— Literary Hub, Literary Hub, 10 July 2026

Definition of dead

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“Deadly.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/deadly. Accessed 16 Jul. 2026.

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