Barrel tax (3)
I believe the answer is:
I believe this is a double definition.
'barrel' is the first definition.
(I've seen this before)
'tax' is the second definition.
(UK Value Added Tax)
(Other definitions for vat that I've seen before include "Large tank or vessel" , "Large container for liquid" , "Fermentation vessel" , "Large tub; tax" , "Container for liquids" .)