Trust in secrecy (10)
I believe the answer is:
confidence
'trust in secrecy' is the definition.
'confidence' can be an answer for 'trust' (synonyms). I'm unsure of the 'in secrecy' bit.
'trust in secrecy' is the wordplay.
'trust' becomes 'confide' (synonyms).
'in secrecy' becomes 'nce' (I can't justify this - if you can you should give a lot more credence to this answer).
'confide'+'nce'='CONFIDENCE'
Can you help me to learn more?
(Other definitions for confidence that I've seen before include "Shared secret - belief" , "courage" , "Trust" , "communication of faith" , "belief in one's own abilities" .)