# lethal

/ˈɫiθəɫ/ (US) · /lˈiːθəl/ (UK)

Source: https://englishreference.com/word/lethal
Updated: 2026-06-20

## Senses

### 1. deadly

adjective · CEFR B2

able to cause death.

For teachers: capable of causing death; fatal or mortal in effect.

- The snake's venom is lethal to small animals and humans.
- The laboratory confirmed that the chemical spill contained a lethal concentration of toxins, necessitating an immediate evacuation of the surrounding area.

### 2. very effective or dangerous

adjective · CEFR C1 · Informal

extremely successful or powerful, often in a way that defeats an opponent.

For teachers: highly effective or devastating in a figurative sense, particularly regarding skill or performance.

- The striker has a lethal shot that most goalkeepers cannot stop.
- Her lethal wit and sharp debating skills made her a formidable opponent in the courtroom.

### 3. a deadly gene

noun · CEFR C2 · Technical

a version of a gene that causes an organism to die.

For teachers: an allele that causes the death of the organism that carries it, often before birth or maturity.

- The researchers studied how a specific lethal gene was passed down in the fruit flies.
- The presence of a homozygous lethal in the population resulted in a significant deviation from the expected Mendelian ratios among the surviving offspring.

### 4. a chemical compound

noun · CEFR C2 · Technical

a type of solid alcohol found in certain oils and waxes.

For teachers: one of the higher alcohols of the paraffin series, typically obtained from spermaceti as a white crystalline solid.

- The chemist isolated the lethal from the wax sample for further testing.
- The structural analysis of the lethal revealed a long-chain aliphatic alcohol consistent with derivatives of spermaceti.

## Examples

- The snake's bite contains a lethal dose of venom.
- The factory was evacuated immediately after a lethal gas leak was detected in the main laboratory.
- While the individual chemicals are relatively harmless, their combination creates a lethal reaction that requires specialized containment protocols to ensure the safety of the research staff.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.