Circumspect (7)
'circumspect' is the definition.
(synonyms)
This is all the clue.
(Other definitions for discreet that I've seen before include "Diplomatic" , "Cautious, doesn't give away secrets" , "Showing prudence and circumspection" , "Tactful and trustworthy" , "Doesn't give away secrets - can be trusted" .)
'circumspect' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for prudent that I've seen before include "Acting with care for the future" , "Thinking of the future" , "not taking any risks?" , "Wise and cautious" , "Cautious and circumspect" .)