Empty container inside a different one (6)
I believe the answer is:
vacant
'empty' is the definition.
(similar in meaning)
'container inside a different one' is the wordplay.
'container' becomes 'can' (can is a kind of container).
'inside' indicates putting letters inside.
'a different one' becomes 'vat' (I can't explain this - if you can you should give a lot more credence to this answer).
'can' placed inside 'vat' is 'VACANT'.
Can you help me to learn more?
(Other definitions for vacant that I've seen before include "Horse in a race" , "Without an occupant or incumbent" , "Unoccupied - unthinking" , "available" , "unemployed" .)