Worker supports subordinate revealing secret (9)
I believe the answer is:
underhand
'secret' is the definition.
(underhand means secret or duplicitous)
'worker supports subordinate' is the wordplay.
'worker' becomes 'hand' (hand is a kind of worker).
'supports' means one lot of letters go next to another (bottom letters provide a support for the top ones).
'subordinate' becomes 'under' (similar in meaning).
'hand' after 'under' is 'UNDERHAND'.
'revealing' is the link.
(Other definitions for underhand that I've seen before include "servant of lower rank" , "Crafty" , "Unsporting" , "Reporting to worker" , "In a secret or dishonest way" .)