Small cask or barrel (3)
I believe the answer is:
keg
This clue is a double definition.
'small cask' is the first definition.
(I've seen this in another clue)
'barrel' is the second definition.
(I know that keg is a type of barrel)
(Other definitions for keg that I've seen before include "Small beer cask" , "What's found at King's Head" , "Barrel as for beer" , "Sort of beer" , "Small cask or barrel" .)