Nehushtan

Nehushtan - of copper; a brazen thing a name of contempt given to the serpent Moses had made in the wilderness (Num. 21:8), and which Hezekiah destroyed because the children of Israel began to regard it as an idol and "burn incense to it." The lapse of nearly one thousand years had invested the "brazen serpent" with a mysterious sanctity; and in order to deliver the people from their infatuation, and impress them with the idea of its worthlessness, Hezekiah called it, in contempt, "Nehushtan," a brazen thing, a mere piece of brass (2 Kings 18:4).

From Easton's Bible Dictionary (1897)