Complain at vehicle parking (4)
I believe the answer is:
carp
'complain' is the definition.
(thesaurus)
'at vehicle parking' is the wordplay.
'at' says to put letters next to each other.
'vehicle' becomes 'car' (car is a kind of vehicle).
'parking' becomes 'p'.
'car' put next to 'p' is 'CARP'.
(Other definitions for carp that I've seen before include "Criticise - fish" , "Complain in manner of goldfish" , "Fish - make captious criticism" , "Fish often kept in ponds" , "Fish - complain" .)