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

Also known as the "poison parsnip", hemlock water dropwort - Oenanthe crocata - is one of the most poisonous plants native to the UK.

From BBC • Jul. 10, 2023

Stonecipher was the first in a line of future Boeing CEOs influenced by General Electric’s Jack Welch, one of the most poisonous individuals in American business since the robber barons.

From Seattle Times • May 13, 2022

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