Small cask (3)
I believe the answer is:
keg
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">small cask</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for keg that I've seen before include "Small cask or barrel" , "Barrel as for beer" , "What's found at King's Head" , "Small beer cask" , "Sort of beer" .)