Bullion bar (5)
I believe the answer is:
ingot
'bullion bar' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ingot that I've seen before include "Metallic bar" , "A lump of metal, perhaps gold" , "Piece of cast metal" , "Mass of cast metal" , "Block (of steel, gold, etc)" .)