Shares making a comeback for single master (5)
I believe the answer is:
sloop
'single master' is the definition.
(type of ship with one mast)
'shares making a comeback' is the wordplay.
'shares' becomes 'pools' (pooling is a kind of sharing).
'making a comeback' says the letters should be written backwards.
'pools' back-to-front is 'SLOOP'.
'for' is the link.
(Other definitions for sloop that I've seen before include "Sailboat" , "Vessel with a single mast" , "One-masted sailing boat" , "Type of sailing boat" , "One-masted sailing ship" .)