Son to manage range (5)
I believe the answer is:
scope
'range' is the definition.
('scope' can be a synonym of 'range')
'son to manage' is the wordplay.
'son' becomes 's'.
'to manage' becomes 'cope' ('cope' can be a synonym of 'manage').
's'+'cope'='SCOPE'
(Other definitions for scope that I've seen before include "Space for movement or activity" , "Range of action" , "Extent or reach" , "Charity" , "Range, compass" .)