What is a…
cockatrice

Cockatrice his is the medieval 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 14:29 KJV; Isaiah 59:5 KJV; Jeremiah 8:17 KJV; in all which the Revised King James Version renders the Hebrew tziph'oni by “basilisk”).

…from the serpent’s root a viper will come out… —Isaiah 14:29 NASB excerpt

They hatch adders’ eggs and weave the spider’s web;
He who eats of their eggs dies,
And from that which is crushed a snake breaks forth. —Isaiah 59:5 NASB

For behold, I will send serpents among you,
Vipers which cannot be charmed,
And they shall bite you,” says the Lord. —Jeremiah 8:17 NKJV

In Proverbs 23:32 the Hebrew tzeph'a is rendered both in the King James Version and the Revised King James Version by “adder;” margin of Revised King James Version “basilisk,” and of King James Version “cockatrice.”