lethal

1 of 3

adjective

le·​thal ˈlē-thəl 

1

a

: of, relating to, or causing death

death by lethal injection

b

: capable of causing death

lethal chemicals

2

: gravely damaging or destructive : devastating

a lethal attack on his reputation

3

: very potent or effective

a lethal fastball

also : having a high alcohol content

a lethal rum punch

lethality

lē-ˈtha-lə-tē 

noun

lethally

ˈlē-thə-lē 

adverb

lethal

2 of 3

noun (1)

1

: an abnormality of genetic origin causing the death of the organism possessing it

2

: lethal gene

lethality

3 of 3

noun (2)

le·​thal·​i·​ty lēˈthalətē 

plural -es

: the quality or state of being lethal : deadliness

modern weapons have greater range, accuracy, speed, and lethality than anything ever dreamed of before

—W. P. Corderman

Synonyms of lethal

Adjective

• deadly
• fatal
• poisonous

Choose the Right Synonym for lethal

deadly, mortal, fatal, lethal mean causing or capable of causing death.

deadly applies to an established or very likely cause of death.

a deadly disease

mortal implies that death has occurred or is inevitable.

a mortal wound

fatal stresses the inevitability of what has in fact resulted in death or destruction.

fatal consequences

lethal applies to something that is bound to cause death or exists for the destruction of life.

lethal gas

Examples of lethal in a Sentence

Adjective

a potentially lethal dose of a drug

He was sentenced to death by lethal injection.

Recent Examples on the Web

Adjective

Over a decade, more than 1,000 people have died across the country after police subdued them through means not intended to be lethal, such as physical holds, Tasers and body blows, an investigation led by The Associated Press found. — Hannah Fingerhut, Chicago Tribune, 26 June 2026

Haiti later won a true goal thanks to a lethal shot from Isidor. — Marlene Lenthang, NBC news, 25 June 2026

Noun

Like coolant, antifreeze is a lethal for dogs and cats. — Alexis Simmerman, Austin American Statesman, 16 Dec. 2025

Almost 8 of 10 lethal overdose victims had no contact with the agency before their deaths, the report found. — Washington Post, 4 Sep. 2020

Word History

Etymology

Adjective

borrowed from Latin lētālis, lēthālis, from lētum, lēthum "death, especially when brought about violently" (of uncertain origin) + -ālis -al entry 1

Note: The variant spellings with -h- are presumably by association with Greek lḗthē "forgetfulness, oblivion" (see lethe).

Noun (1)

derivative of lethal entry 1

First Known Use

Adjective

circa 1604, in the meaning defined at sense 1a

Noun (1)

1917, in the meaning defined at sense 1

Phrases Containing lethal

• lethal gene

Rhymes for lethal

• nonlethal
• sublethal

Kids Definition

lethal

1 of 2 adjective

le·​thal ˈlē-thəl 

: causing or capable of causing death

lethal chemicals

lethally

ˈlē-thə-lē 

adverb

lethal

2 of 2 noun

: lethal gene

Medical Definition

lethal

1 of 2 adjective

le·​thal ˈlē-thəl 

: of, relating to, or causing death

a lethal injury

also : capable of causing death

lethal chemicals

a lethal dose

lethality

lē-ˈthal-ət-ē 

noun

plural lethalities

lethally adverb

lethal

2 of 2 noun

1

: an abnormality of genetic origin causing the death of the organism possessing it usually before maturity

2

: lethal gene