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.

   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.

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

   Antonyms: nonpoisonous, unpoisonous

2. (figuratively) Negative, harmful.
   • 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.

   Synonym: toxic

Some speakers make a distinction between poisonous (releasing toxins when eaten), and venomous (releasing toxins (known as venom in this case) by biting a target), especially in non-colloquial speech.