Jacob's missus maybe runs vessel (4)
I believe the answer is:
ewer
'vessel' is the definition.
(ewer is a kind of vessel)
'jacob's missus maybe runs' is the wordplay.
'jacob's missus maybe' becomes 'ewe' (female sheep - Jacob is a type of sheep).
'runs' becomes 'r' (cricket abbreviation).
'ewe'+'r'='EWER'
(Other definitions for ewer that I've seen before include "Container" , "Large, wide-mouthed jug" , "Large water jug" , "Large water-jug" , "water-carrier" .)