The last letter in ‘c’ is a metal (4)
I believe the answer is:
zinc
'is a metal' is the definition.
(I've seen this before)
'the last letter in c' is the wordplay.
'the last letter' becomes 'z' (last letter of the alphabet).
'z'+'in'+'c'='ZINC'
(Other definitions for zinc that I've seen before include "Metal alloyed with copper to make brass" , "Metal used in brass" , "Blusish-white lustrous metallic element" , "Metal, Zn" , "Metal much used in alloys" .)