Corrosion-resistant metal (7)
I believe the answer is:
iridium
'corrosion-resistant metal' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for iridium that I've seen before include "Colourful compounds come from this" , "Heavy corrosion-resistant metal, used in alloys" , "Hard silvery metal" , "Silvery-white metallic element" , "number 77" .)