From Wiktionary, the free dictionary
From tossigo (“venom, poison”) + -oso.
tossigoso m (feminine tossigosa, masculine plural tossigosos, feminine plural tossigosas)
- (of an animal) venomous, toxic
c. 1250, Alfonso X, Lapidario, f. 15v:Su uertud es atal que preſta contra todos los toſſicos mortales. ⁊ feridas o mordeduras de beſtias toſſigoſas.- Its virtue is such that it is useful against all the lethal venoms, and the wounds or bite marks of venomous beasts.
- (of a thing or substance) toxic, poisonous