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most poisonous

ADJECTIVE

harmful

Synonyms

WEAK

bad baleful baneful corrupt corruptive dangerous deadly deleterious destructive detrimental evil fatal hurtful infective lethal malicious malignant mephitic miasmatic morbid mortal nocuous noisome noxious peccant pernicious pestiferous pestilential septic toxic toxicant toxiferous venomous vicious viperous virulent

Antonyms

WEAK

aiding antidotal assisting curing healing helpful

ADJECTIVE

harmful

Synonyms

STRONGEST

dangerous deadly destructive fatal lethal noxious pernicious toxic venomous vicious virulent

WEAK

bad baleful baneful corrupt corruptive deleterious detrimental evil hurtful infective malicious malignant mephitic miasmatic morbid mortal nocuous noisome peccant pestiferous pestilential poison septic toxicant toxiferous viperous

Antonyms

STRONGEST

gentle good harmless healthful healthy helpful kind life-giving nice nonpoisonous wholesome

WEAK

benevolent non-toxic

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

The death cap is the world’s most poisonous mushroom, responsible for 90% of mushroom-related fatalities.

From Los Angeles Times • Jan. 16, 2026

"The most poisonous water has to flow down and mix with the healthy water."

From BBC • Aug. 26, 2022

Death cap mushrooms, among the most poisonous in the world, closely resemble Poland’s popular, edible parasol mushroom.

From Seattle Times • Aug. 31, 2021

The Portrait of a Lady by Henry James A young woman’s auspicious future and personal autonomy is destroyed by one of the most poisonous men in fiction.

From The Guardian • Jan. 8, 2020

“Jellyfish are really mysterious to me. The most poisonous one in the world is the size of a gnat or something.”

From "Ivy Aberdeen’s Letter to the World" by Ashley Herring Blake