poisonous

From Middle English poisounous, poysonouse, equivalent to poison +‎ -ous.

• IPA^(key): /ˈpɔɪzənəs/, /ˈpɔɪznəs/

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• Rhymes: -ɔɪzənəs, -ɔɪznəs

poisonous (comparative more poisonous, superlative most poisonous)

1. Containing sufficient poison to be dangerous to touch or ingest.

   Synonyms: poisoned, toxic, venomous, (dialectal or archaic) attery

   Antonyms: nonpoisonous, unpoisonous

   While highly poisonous to dogs, this substance is completely harmless if ingested by humans.

   • 1757, John Dyer, “Book I”, in The Fleece: A Poem […] ‎, London: R. and J. Dodsley, page 40:

     Nor taint-worm ſhall infect the yeaning herds / Nor penny-graſs, nor ſpearwort's poiſ'nous leaf.

   • 2003, Charles L. Fergus, Common Edible and Poisonous Mushrooms of the Northeast, Stackpole Books, →ISBN, page 77:

     I had picked a mushroom so poisonous that particles of it, stuck to my fingers and accidentally swallowed, could have made me deathly ill, and a piece the size of my thumb could have killed me.

2. (figuratively) Negative, harmful.

   Synonym: toxic

   • 2013, Kylie Griffin, Allegiance Sworn, Penguin, →ISBN:

     He didn't want to end up like his grandfather, bitter and intractable, consumed in his hatred like an addict on haze — a poisonous attitude that would possess him all his remaining years.

Some speakers, especially in technical contexts, make a distinction between poisonous (releasing toxins when eaten), and venomous (releasing toxins (known as venom in this case) by biting or stinging a target).