noble metal definition by American Heritage Dictionary
The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
A metal or alloy, such as gold, that is highly resistant to oxidation and corrosion.
noble metal definition by Wiktionary
(plural noble metals)
So termed because they resist being made base. Metals that chemist recognize as the platinum group of elements.