In European bestiaries and legends, a basilisk (ˈbæsɪlɪsk or ˈbæzɪlɪsk) is a legendary reptile reputed to be a serpent king, who causes death to those who look into its eyes. According to the Naturalis Historia of Pliny the Elder, the basilisk of Cyrene is a small snake, "being not more than twelve inches in length", that is so venomous, it leaves a wide trail of deadly venom in its wake, and its gaze is likewise lethal.
The basilisk's weakness is the odor of the weasel, which, according to Pliny, was thrown into the basilisk's hole, recognizable because some of the surrounding shrubs and grass had been scorched by its presence. It is possible that the legend of the basilisk and its association with the weasel in Europe was inspired by accounts of certain species of Asiatic snakes (such as the king cobra) and their natural predator, the mongoose.
The word originates from the Greek form basilískos (βασιλίσκος; basiliscus), which means "little king", "little prince", "chieftain", or "young ruler", from two components, βᾰσῐλεύς (basileús, “king”) and -ῐ́σκος (-ískos, diminutive). It was also considered to be synonymous with the cockatrice.
The basilisk is called "king" because it is reputed to have on its head a mitre, or crown-shaped crest. Stories of the basilisk show that it is not completely distinguished from the cockatrice. The basilisk is alleged to be hatched by a cockerel from the egg of a serpent or toad (the reverse of the cockatrice, which was hatched from a cockerel's "egg" incubated by a serpent or toad). In Medieval Europe, the description of the creature began taking on features from cockerels. It has a venomous strike, and in some versions of the myth, it has the ability to breathe fire.
One of the earliest accounts of the basilisk comes from Pliny the Elder's Natural History, written in roughly 79 AD. He describes the catoblepas, a monstrous cow-like creature of which "all who behold its eyes, fall dead upon the spot", and then goes on to say,
There is the same power also in the serpent called the basilisk.