A mythological serpent, reputed to have hatched from a rooster's egg and capable of killing man and beast with its stare. Also known as basilisk.

Mischiefs are like a cockatrice's eye; if they see first, they kill; if seen, they die.
John Dryden

14th century. Via Old French cocatris from medieval Latin calcatrix, "tracker" from Latin calcare, "to track."