This word occurs in the Authorized Version. But brass is a factitious metal, not known to the early Hebrews, and wherever it occurs, copper is to be understood [COPPER]. That copper is meant is shown by the text, 'Out of whose hills thou mayest dig brass' (Deuteronomy 8:9), it being of course impossible to dig a factitious metal, whether brass or bronze, out of mines.
Brass (to retain the word) is in Scripture the symbol of insensibility, baseness, and presumption or obstinacy in sin (Isaiah 48:4; Jeremiah 6:28; Ezekiel 22:18). Brass is also a symbol of strength (Psalms 107:16; Isaiah 48:4; Micah 4:13). So in Jeremiah 1:18; Jeremiah 15:20, brazen walls signify a strong and lasting adversary or opponent.