Bar return of vessels (4)
I believe the answer is:
stop
'bar' is the definition.
(thesaurus)
'return of vessels' is the wordplay.
'return of' says the letters should be written in reverse.
'vessels' becomes 'pots' (pot is a kind of vessel).
'pots' in reverse letter order is 'STOP'.
(Other definitions for stop that I've seen before include "Refrain from" , "Pack it in - bar" , "Standstill" , "Quit" , "Knock out" .)