Private's not to win in court (6)
I believe the answer is:
closet
'private's' is the definition.
(similar in meaning)
'not to win in court' is the wordplay.
'not to win' becomes 'lose' ('lose' is the opposite to 'win').
'in' is an insertion indicator.
'court' becomes 'ct' (abbreviation used in road names).
'lose' put inside 'ct' is 'CLOSET'.
(Other definitions for closet that I've seen before include "Wardrobe in the US" , "Small cupboard or recess" , "Secret - cupboard" , "secret is revealed" , "A small room - best to come out of it" .)