Large beer cask (3)
I believe the answer is:
tun
'large beer cask' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tun that I've seen before include "Barrel holding many gallons" , "Large cask (holding 252 gallons)" , "Cask, vat" , "Large cask for liquid" , "One can hold wine" .)