Vessel used by the werewolf (4)
I believe the answer is:
ewer
'vessel' is the definition.
(ewer is a kind of vessel)
'used by the werewolf' is the wordplay.
'used by' says the answer is hidden in the clue.
'EWER' is hidden in the letters of 'the werewolf'.
(Other definitions for ewer that I've seen before include "Big jug" , "29 [VESSEL]" , "Vessel for pouring" , "Jar for water" , "Large pitcher" .)