King James Bible Dictionary

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).

a trifling thing of brass

The brazen serpent.
2 Kings 18:4

(a thing of brass), the name by which the brazen serpent made by Moses in the wilderness, (Numbers 21:9) was worshipped in the time of Hezekiah. (2 Kings 18:4) It is evident that our translators by their rendering "and he called it Nehushtan" understood that the subject of the sentence is Hezekiah and that when he destroyed the brazen serpent he gave it the name Nehushtan "a brazen thing" in token of his utter contempt. But it is better to understand the Hebrew as referring to the name by which the serpent was generally known, the subject of the verb being indefinite

"and one called it 'Nehushtan.'"