Poles supporting own harbours (6)
I believe the answer is:
havens
'harbours' is the definition.
('haven' can be a synonym of 'harbour')
'poles supporting own' is the wordplay.
'poles' becomes 'NS' (north and south poles).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'own' becomes 'have' (synonyms).
'ns' put after 'have' is 'HAVENS'.
(Other definitions for havens that I've seen before include "Asylums" , "Places of safety or sanctuary" , "'Shelters, sanctuaries (6)'" .)