Speculation in gold concealed by people in general (6)
I believe the answer is:
theory
'speculation' is the definition.
(I've seen this before)
'gold concealed by people in general' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'concealed by' means one lot of letters goes inside another.
'people in general' becomes 'they' (I've seen this in another clue).
'or' placed into 'they' is 'THEORY'.
'in' is the link.
(Other definitions for theory that I've seen before include "Conjectural view" , "The words, as opposed to the practice" , "Series of ideas seeking to explain something" , "Guess" , "Justifying hypothesis" .)