Public duck enclosure (4)
I believe the answer is:
open
'public' is the definition.
(associated in meaning)
'duck enclosure' is the wordplay.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'enclosure' becomes 'pen' (pen is a kind of enclosure).
'o'+'pen'='OPEN'
(Other definitions for open that I've seen before include "simple" , "Candid - ready for business" , "Without concealment" , "Unrestricted; ready for business" , "Agape" .)