The mediaeval name (a corruption of "crocodile") of a fabulous serpent supposed to be produced from a cock's egg. It is generally supposed to denote the cerastes, or "horned viper," a very poisonous serpent about a foot long. Others think it to be the yellow viper (Daboia xanthina), one of the most dangerous vipers, from its size and its nocturnal habits (Isaiah 11:8; 14:29; 59:5; Jeremiah 8:17; in all which the Revised Version renders the Hebrew tziph'oni by "basilisk"). In Proverbs 23:32 the Hebrew tzeph'a is rendered both in the Authorized Version and the Revised Version by "adder;" margin of Revised Version "basilisk," and of Authorized Version "cockatrice."

Noah Webster's New International Dictionary of the English Language

1. (n.) A fabulous serpent whose breath and look were said to be fatal. See Basilisk.

2. (n.) A representation of this serpent. It has the head, wings, and legs of a bird, and tail of a serpent.

3. (n.) A venomous serpent which cannot now be identified.

4. (n.) Any venomous or deadly thing.