It's one of twenty-six he leases (6)
I believe the answer is:
letter
I believe this clue is a double definition.
'it's one of twenty-six' is the first definition.
(I've seen this before)
'he leases' is the second definition.
(I've seen this before)
(Other definitions for letter that I've seen before include "An alphabetic unit" , "he leases" , "Epistle, missive" , "Form of correspondence" , "A written form of communication" .)