A northern set with southern backers (6)
I believe the answer is:
angels
'backers' is the definition.
('angel' can be a synonym of 'backer')
'a northern set with southern' is the wordplay.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'set' becomes 'gel' (both can mean to harden).
'with' means one lot of letters go next to another.
'southern' becomes 's' (abbreviation).
'a'+'n'+'gel'+'s'='ANGELS'
(Other definitions for angels that I've seen before include "Heavenly beings" , "Financial backers, esp theatrical" , "Thrones maybe" , "Cherubim, seraphim etc" , "Ministering spirits" .)