Of copper; a brazen thing a name of contempt given to the serpent Moses had made in the wilderness (Numbers 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).

Noah Webster's New International Dictionary of the English Language

(n.) A thing of brass; -- the name under which the Israelites worshiped the brazen serpent made by Moses.