Apparently passive participle of H5172 (perhaps in the sense of {ringing} that {is} bell metal; or from the red color of the throat of a serpent ({H5175} as denominative) when hissing); {coppery} that {is} (figuratively) hard: - of brass.
Isa 45:2I will go before thee, and make the crooked places straight: I will break in pieces the gates of brassH5154, and cut in sunder the bars of iron:
Mic 4:13Arise and thresh, O daughter of Zion: for I will make thine horn iron, and I will make thy hoofs brassH5154: and thou shalt beat in pieces many people: and I will consecrate their gain unto the LORD, and their substance unto the Lord of the whole earth.