From an unused root. Nechōshet refers to copper in its pure form and bronze (copper-tin alloy) as a worked metal. It was one of the most important metals of the ancient world, used extensively in the Tabernacle and Temple furnishings. The word is sometimes translated brass (older versions) though true brass is copper-zinc.
Bronze (nechōshet) in the Tabernacle and Temple carried profound theological symbolism. The Bronze Altar (Ex. 27:2) — where all burnt offerings and sin offerings were made — stood at the entrance to the Tabernacle, the first thing one encountered. No worshiper could approach God without first confronting the altar — and its bronze surface spoke of judgment endured, fire withstood. The Bronze Laver (Ex. 30:18) stood between the altar and the Tent — washing for service. Together, these bronze furnishings declared that access to God requires atonement and purification. In Numbers 21, the Bronze Serpent (nachash nechōshet) — the serpent on a pole — became an instrument of healing, which Jesus Himself interpreted as a type of His own crucifixion (John 3:14). What had been an instrument of death (the serpent) was lifted up and became the source of life — just as what was the ultimate symbol of curse (the cross) became the source of salvation.