Empty vat can be overturned (6)
I believe the answer is:
vacant
'empty' is the definition.
('vacant' can be similar in meaning to 'empty')
'vat can be overturned' is the wordplay.
'be overturned' indicates an anagram.
'vat'+'can'='vatcan'
'vatcan' anagrammed gives 'VACANT'.
(Other definitions for vacant that I've seen before include "Empty, not occupied" , "unemployed" , "Unoccupied - unthinking" , "Empty - stupid" , "available" .)