Were released from jug (4)
I believe the answer is:
ewer
'jug' is the definition.
(type of vessel)
'were released' is the wordplay.
'released' indicates an anagram (letters released from their original order).
'were' with letters rearranged gives 'EWER'.
'from' acts as a link.
(Other definitions for ewer that I've seen before include "Open vessel with handle and spout" , "from which liquid may be poured" , "Jar for water" , "Were (anag)" , "Large water-jug" .)