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Definitions

poisonous

[poi-zuh-nuhs] / ˈpɔɪ zə nəs /
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.

It’s got poisonous lead in it from paint.

From Salon • Mar. 6, 2026

But there are dozens of other poisonous snake species for which India does not have targeted antivenom.

From BBC • Feb. 1, 2026

But time and again the poisonous isolation that absolute power imposes on its wielders blunted the edge of their insight and degraded the capacity of their societies.

From The Wall Street Journal • Jan. 26, 2026

Hydrogen cyanide, which is highly poisonous, can freeze into crystals at low temperatures.

From Science Daily • Jan. 16, 2026

It made him think of a large, poisonous spider that was out to catch him.

From "Shooting Kabul" by N. H. Senzai

From Roget's 21st Century Thesaurus, Third Edition Copyright © 2013 by the Philip Lief Group.