Harbours possess poles (6)
I believe the answer is:
havens
'harbours' is the definition.
('haven' can be a synonym of 'harbour')
'possess poles' is the wordplay.
'possess' becomes 'have' (synonyms).
'poles' becomes 'NS' (north and south poles).
'have'+'ns'='HAVENS'
(Other definitions for havens that I've seen before include "Asylums" , "'Shelters, sanctuaries (6)'" , "Places of safety or sanctuary" .)