Discretion in charge of gambit (6)
I believe the answer is:
tactic
'gambit' is the definition.
(thesaurus)
'discretion in charge' is the wordplay.
'discretion' becomes 'tact' (I've seen this before).
'in charge' becomes 'ic'.
'tact'+'ic'='TACTIC'
'of' acts as a link.
(Other definitions for tactic that I've seen before include "Stratagem, procedure" , "Action designed to achieve a specific end" , "Strategy carefully planned to achieve a specific end" , "element of strategy" , "Manoeuvre designed to outwit enemy" .)