Son to manage range (5)
I believe the answer is:
scope
'range' is the definition.
(synonyms)
'son to manage' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'to manage' becomes 'cope' (manage can mean to cope or do well).
'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" .)