noble metal vs gold

noble metal and gold both are nouns.

Word	Noun	Adjective	Verb	Adverb
noble metal	Yes	No	No	No
gold	Yes	Yes	No	No

As nouns, gold is a hyponym of noble metal; that is, gold is a word with a more specific, narrower meaning than noble metal:

noble metal: any metal that is resistant to corrosion or oxidation
gold: a soft yellow malleable ductile (trivalent and univalent) metallic element; occurs mainly as nuggets in rocks and alluvial deposits; does not react with most chemicals but is attacked by chlorine and aqua regia

Other hyponyms of noble metal include atomic number 79, Au, atomic number 78, platinum, Pt, Ag, atomic number 47, silver.

noble metal (noun)	gold (noun)
any metal that is resistant to corrosion or oxidation	a deep yellow color
	something likened to the metal in brightness or preciousness or superiority etc.
	coins made of gold
	great wealth
	a soft yellow malleable ductile (trivalent and univalent) metallic element; occurs mainly as nuggets in rocks and alluvial deposits; does not react with most chemicals but is attacked by chlorine and aqua regia

noble metal (adjective)	gold (adjective)
	having the deep slightly brownish color of gold
	made from or covered with gold