Mean, to say 'mature' (7)
I believe the answer is:
average
'mean' is the definition.
('average' can be a synonym of 'mean')
'say mature' is the wordplay.
'say' becomes 'aver' ('aver' can be a synonym of 'say').
'mature' becomes 'age' ('age' can be a synonym of 'mature').
'aver'+'age'='AVERAGE'
'to' acts as a link.
(Other definitions for average that I've seen before include "building society customer loses capital over time" , "Middle value, the norm" , "Normal in arithmetic way" , "Mean, median or middling" , "Mean - medium" .)