Nickel, e.g. (4)
(Other definitions for coin that I've seen before include "Metal used as money" , "Money; devise (a word)" , "Invent a word or phrase - for money?" , "Metal currency" , "Invent (a new phrase)" .)
(Other definitions for metal that I've seen before include "Gambling token" , "Copper, perhaps" , "Eg, copper" , "employed in making roads" , "Material detectable in the ground" .)