Metal is able to be used as a container (3,3)
I believe the answer is:
tin can
'a container' is the definition.
(I know that tin can is a type of container)
'metal is able to' is the wordplay.
'metal' becomes 'tin' (tin is a kind of metal).
'is able to' becomes 'can' (if you can do something you are able to do it).
'tin'+'can'='TIN-CAN'
'be used as' acts as a link.
(Other definitions for tin can that I've seen before include "vessel" , "emptied food container" , "Means to preserve" , "container - this one?" , "Metal container" .)