Miss in court reveals secret (6)
I believe the answer is:
closet
'secret' is the definition.
(synonyms)
'miss in court' is the wordplay.
'miss' becomes 'lose' (I've seen this in other clues).
'in' means one lot of letters goes inside another.
'court' becomes 'ct'.
'lose' going into 'ct' is 'CLOSET'.
'reveals' acts as a link.
(Other definitions for closet that I've seen before include "Private room; cupboard" , "A small room or cupboard" , "secret is revealed" , "small compartment for clothing" , "Furtive" .)