Empty tin into large vessel (6)
I believe the answer is:
vacant
'empty' is the definition.
(similar in meaning)
'tin into large vessel' is the wordplay.
'tin' becomes 'can' (synonyms).
'into' is an insertion indicator.
'large vessel' becomes 'vat' (I've seen this before).
'can' placed inside 'vat' is 'VACANT'.
(Other definitions for vacant that I've seen before include "... Blank" , "Unoccupied - unthinking" , "Without an occupant or incumbent" , "Empty - stupid" , "Of house, not occupied at present" .)