Plug vessels the wrong way (4)
I believe the answer is:
stop
'plug' is the definition.
(I've seen this before)
'vessels the wrong way' is the wordplay.
'vessels' becomes 'pots' (pot is a kind of vessel).
'the wrong way' says the letters should be written backwards.
'pots' back-to-front is 'STOP'.
(Other definitions for stop that I've seen before include "Wind up" , "Plug - organ knob - bus halt - period" , "Stay" , "Put off for ever" , "Cease, desist, whoa" .)