Police officer parking in hollow (3)
I believe the answer is:
dip
'hollow' is the definition.
(I've seen this in other clues)
'police officer parking' is the wordplay.
'police officer' becomes 'di' (detective inspector).
'parking' becomes 'p'.
'di'+'p'='DIP'
'in' acts as a link.
(Other definitions for dip that I've seen before include "Depression in a surface" , "See 21" , "Drop" , "Dunk" , "An informal swim or a downward slope" .)