Is able to preserve tin (3)
I believe the answer is:
can
This clue is a triple definition!
'is able to' is the first definition.
(I've seen this before)
'preserve' is the second definition.
(canning is a kind of preserving)
'tin' is the third definition.
(synonyms)
(Other definitions for can that I've seen before include "Possesses ability" , "prison" , "has power" , "Tin; be able to" , "depth charge" .)