platinum vs noble metal

platinum and noble metal both are nouns.

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

As nouns, noble metal is a hypernym of platinum; that is, noble metal is a word with a broader meaning than platinum:

platinum: a heavy precious metallic element; grey-white and resistant to corroding; occurs in some nickel and copper ores and is also found native in some deposits
noble metal: any metal that is resistant to corrosion or oxidation

platinum (noun)	noble metal (noun)
a heavy precious metallic element; grey-white and resistant to corroding; occurs in some nickel and copper ores and is also found native in some deposits	any metal that is resistant to corrosion or oxidation