Is able to preserve (3)
I believe the answer is:
can
I believe this clue is a double definition.
'is able to' is the first definition.
(if you can do something you are able to do it)
'preserve' is the second definition.
(canning is a kind of preserving)
(Other definitions for can that I've seen before include "prison" , "Is able; container" , "May" , "depth charge" , "Metallic container" .)