Gold lump (6)
I believe the answer is:
nugget
'gold lump' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nugget that I've seen before include "Solid lump of a precious metal" , "Raw lump (of gold)" , "Lump of, eg, gold" , "Something small and precious" , "Lump of gold in natural state" .)