Raid gold in possession of fairy (5)
I believe the answer is:
foray
'raid' is the definition.
(I know that raid can be written as foray)
'gold in possession of fairy' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'in possession of' is an insertion indicator.
'fairy' becomes 'fay' (I've seen this in another clue).
'or' put into 'fay' is 'FORAY'.
(Other definitions for foray that I've seen before include "Depredation" , "Raid for plunder" , "Assault" , "Brief attack" , "Sortie" .)