Worthless metal container (6)
I believe the answer is:
tinpot
'worthless' is the definition.
(tinpot can mean inferior or worthless)
'metal container' is the wordplay.
'metal' becomes 'tin' (tin is a kind of metal).
'container' becomes 'pot' (pot is a kind of container).
'tin'+'pot'='TINPOT'
(Other definitions for tinpot that I've seen before include "of little value" , "Worthless" , "Cheap" , "Petty (dictator etc)" , "Ineffective" .)