poisonous

poisonous — adjective

1. containing poison, or acting like poison, so that a person or animal can become

1.adjectiveB2
Definition

containing poison, or acting like poison, so that a person or animal can become very sick or die when it enters the body.

Example

Several poisonous mushrooms were growing beside the picnic tables in the park.

poisonous + plant/food noun

A warning sign said the factory smoke was poisonous to nearby birds.

be poisonous to + living thing

Common collocations
  • poisonous mushroom
  • poisonous plant
  • poisonous gas
  • poisonous liquid
  • poisonous to dogs
  • poisonous to birds
Synonyms
  • toxic

    broader and slightly more formal; common for chemicals, air, and waste

  • deadly

    emphasizes the risk of death, not specifically poison

  • unsafe

    much broader; can describe danger without poison

Antonyms
  • harmless

    not able to hurt people or animals

  • safe

    general opposite when there is no danger

Grammar Patterns

poisonous + plant/food/substance

be poisonous to + person/animal

Usage Note

Usually said of plants, food, smoke, gas, chemicals, or waste. Distinguish from 'poisoned': poisonous describes something harmful by nature or type, while poisoned describes something that poison was put into.

Common Mistakes

Someone poisoned mushrooms grow behind the cabin.
Poisonous mushrooms grow behind the cabin.
'poisonous' describes something naturally harmful; 'poisoned' means poison was added.

2. describing an animal or insect that makes poison in its body and uses it to prot

2.adjectiveB2
Definition

describing an animal or insect that makes poison in its body and uses it to protect itself or harm another creature.

Example

Bright frogs in this forest are poisonous, so children never touch them.

animal subject + be poisonous

The guide warned us that one small island spider was poisonous.

Common collocations
  • poisonous frog
  • poisonous spider
  • poisonous fish
  • poisonous caterpillar
  • poisonous to handle
Synonyms
  • venomous

    more exact in biology for animals that inject poison by biting or stinging

  • toxic

    broader and more formal; not especially tied to animals

  • dangerous

    much wider; danger may come from size, speed, or attack, not poison

Antonyms

Grammar Patterns

poisonous + animal/insect noun

be poisonous to touch

Usage Note

Subject is usually an animal, insect, fish, or similar creature. Everyday English often uses this word where a biologist might prefer 'venomous', especially for animals that bite or sting. Distinguish from sense 1 (CAUSES POISONING): sense 1 is mostly about plants, food, or substances.

Common Mistakes

The spider was poisoned, so stay back.
The spider was poisonous, so stay back.
'poisoned' means poison was put into it; 'poisonous' describes an animal that carries poison.

3. extremely nasty in attitude, words, or atmosphere, showing a strong wish to hurt

3.adjectiveC1
Definition

extremely nasty in attitude, words, or atmosphere, showing a strong wish to hurt someone.

Example

After the divorce hearing, the room turned poisonous and nobody shook hands.

turn poisonous = become hostile

Marcus sent a poisonous email to his brother after the money argument.

poisonous + words/message noun

Common collocations
  • poisonous remark
  • poisonous email
  • poisonous look
  • poisonous gossip
  • poisonous atmosphere
Synonyms
  • malicious

    more formal; stresses an intention to harm

  • bitter

    focuses more on anger and resentment than active harm

  • toxic

    modern and broader; common for relationships or workplaces

  • nasty

    more everyday and slightly less intense

Antonyms
  • kind

    showing care rather than hostility

  • friendly

    creating a warm and welcoming feeling

Grammar Patterns

poisonous + remark/email/look

grow/turn poisonous

Usage Note

Common with nouns for language and atmosphere, such as remark, letter, rumor, relationship, and silence. Distinguish from senses 1 and 2: this sense is figurative and describes hostility, not real poison.

Common Mistakes

The meeting became poison after the vote.
The meeting became poisonous after the vote.
use the adjective after a linking verb when describing a hostile atmosphere.

Word family

Synonym discussion

Sense: adjective/1

'Poisonous', 'toxic', 'venomous', and 'deadly' all describe danger, but they are not interchangeable. 'Poisonous' is the clearest everyday word for something that can make you ill or kill you if it gets into your body, especially plants, food, mushrooms, or animals. 'Toxic' is broader and slightly more formal; it is common for chemicals, air, and waste, and it also has modern figurative uses such as a toxic workplace. 'Venomous' is narrower: it is used for animals that inject poison by biting or stinging. 'Deadly' only tells you the danger can kill; it does not itself mean poison. Compare: 'Those berries are poisonous', 'The river was polluted with toxic waste', 'That spider is venomous', and 'The fire produced deadly smoke.'

poisonous ↗toxic ↗venomousdeadly ↗

Common collocations

Adverbs

  • highly poisonous
  • extremely poisonous

Phrases

  • turn poisonous
  • grow poisonous

Prepositions

  • poisonous to humans
  • poisonous to animals

Etymology

LatinOld FrenchMiddle EnglishModern English

'Poisonous' was formed in English from 'poison' and the adjective ending '-ous', meaning 'full of' or 'having'. 'Poison' came into Middle English from Old French and goes back to Latin 'potionem', originally meaning 'a drink' or 'dose'. Over time that older word narrowed from something taken as a drink or medicine to something harmful taken into the body. The modern adjective keeps that core idea and later extended to people, words, and situations that seem harmful in an emotional or social way.