Moderate son getting a great deal (6)
I believe the answer is:
soften
'moderate' is the definition.
('soften' can be a synonym of 'moderate')
'son getting a great deal' is the wordplay.
'son getting' becomes 's' (I've seen this in other clues).
'a great deal' becomes 'often' (I've seen this before).
's'+'often'='SOFTEN'
(Other definitions for soften that I've seen before include "become less rough" , "Temper" , "Make less firm" , "Yield" , "Make less hard or become less severe" .)