Those people hoarding gold for speculation (6)
I believe the answer is:
theory
'for speculation' is the definition.
(something theorised or speculated)
'those people hoarding gold' is the wordplay.
'those people' becomes 'they' (I've seen this in another clue).
'hoarding' is an insertion indicator.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'they' going around 'or' is 'THEORY'.
(Other definitions for theory that I've seen before include "Suggested explanation" , "Set of principles on which practice is based" , "Proposition, thesis" , "Ideal situation" , "Explanation of a phenomenon" .)