Cask (3)
'cask' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for barrel that I've seen before include "VAT?" , "Round wooden vessel." , "Large round container as for beer" , "Cheerful old song: 'Roll out the . . . . . .'" , "Beer cask" .)
'cask' is the definition.
(I know that tun is a type of cask)
This is all the clue.
(Other definitions for tun that I've seen before include "Large cask or barrel" , "Large cask (holding 252 gallons)" , "beer barrel" , "Container of beer" , "Barrel holding many gallons" .)