Wiktionary
n. (context inorganic chemistry alchemy English) A metal resistant to corrosion, oxidizing and tarnishing, such as gold, platinum, copper and mercury.
WordNet
n. any metal that is resistant to corrosion or oxidation
Wikipedia
In chemistry, the noble metals are metals that are resistant to corrosion and oxidation in moist air (unlike most base metals). The short list of chemically noble metals (those elements upon which almost all chemists agree) comprises ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold.
More inclusive lists include one or more of mercury, rhenium or copper as noble metals. On the other hand, titanium, niobium, and tantalum are not included as noble metals although they are very resistant to corrosion.
While the noble metals tend to be valuable – due to both their rarity in the Earth's crust and their usefulness in areas like metallurgy, high technology, and ornamentation (jewelry, art, sacred objects, etc.) – the terms "noble metal" and " precious metal" are not synonymous.
The term noble metal can be traced back to at least the late 14th century and has slightly different meanings in different fields of study and application. Only in atomic physics is there a strict definition. For this reason there are many quite different lists of "noble metals".
In addition to this term's function as a compound noun, there are circumstances where "noble" is used as an adjective for the noun "metal". A " galvanic series" is a hierarchy of metals (or other electrically conductive materials, including composites and semimetals) that runs from noble to active, and allows one to predict how materials will interact in the environment used to generate the series. In this sense of the word, graphite is more noble than silver and the relative nobility of many materials is highly dependent upon context, as for aluminium and stainless steel in conditions of varying pH.
Usage examples of "noble metal".
Your serious manner proves in the eyes of the worthy that you are cast of noble metal.
Their noble metal steed took one look and dived into a narrow side-valley.
He opened the back of the car with his universal credit key, a computer chip encased in noble metal and banded to his wrist.
It stood about a foot tall, a simple tall cup made of noble metal.
After all, if a human smith makes inanimate metal objects of the base metal iron, why should not a god-smith make far more clever inanimate metal objects of the noble metal gold?
And he'd let her show him, let her tell him, what she'd found-a bronze rod that turned noble metal to dross, an amulet of uncertain value, a rusted knife whose edge could be coaxed to life.