base metal

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry Any metal at the lower end of the electrochemical series that oxidizes readily.
• noun metallurgy The metal to be welded (rather than that used to weld).
• noun A common or inexpensive metal; especially (alchemy) one that was hoped to be transmuted into a precious metal.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a metal that is common and not considered precious