A Creature Born from a Mistranslation

The cockatrice is an accident of language as much as a creature. Medieval Latin used calcatrix (from a verb "to tread") to render a Greek word for the ichneumon, and versions of scripture used it and related words for Hebrew terms for venomous snakes; the word drifted, and by the later Middle Ages a "cockatrice" was understood as a beast hatched from an egg laid by a cock (rooster) and brooded by a serpent or toad, killing with its glance and breath. In this it merged almost completely with the basilisk.

English translations of the Bible, including the King James Version at Isaiah 11:8 and Jeremiah 8:17, print "cockatrice" where the Hebrew has a poisonous serpent, embedding the mistranslation in scripture for English readers. In heraldry the cockatrice took a fixed and vivid form: a two-legged winged creature with the head, comb and wattles of a rooster and the barbed tail of a serpent, distinct in blazon from the wyvern. It is thus a creature assembled almost entirely from philological confusion and heraldic convention, with no coherent mythology of its own behind it.