Central Park with stick that's secret (6)
I believe the answer is:
arcane
'that's secret' is the definition.
(I've seen this in another clue)
'central park with stick' is the wordplay.
'central' means to look at the middle letters.
'with' means one lot of letters go next to another.
'stick' becomes 'cane' (cane is a kind of stick).
The middle of 'park' is 'ar'.
'ar'+'cane'='ARCANE'
(Other definitions for arcane that I've seen before include "Mysterious, understood by few" , "Mysterious, secret or obscure" , "deep" , "Mysterious like a crane" , "Requiring secret or mysterious knowledge" .)