Block of metal (5)
I believe the answer is:
ingot
'block of metal' is the definition.
(synonyms)
This is all the clue.
(Other definitions for ingot that I've seen before include "Mass of unwrought gold, for instance" , "Moulded metal bar" , "Mass of metal, especially gold or silver" , "Cast metal brick" , "Block of, eg, gold" .)