Sagacious, well-mannered for the most part and in charge (7)
I believe the answer is:
politic
'sagacious' is the definition.
('politic' can be similar in meaning to 'sagacious')
'well-mannered for the most part and in charge' is the wordplay.
'well mannered' becomes 'polite' (I've seen this before).
'for the most part' means to remove the last letter.
'and' is a charade indicator (letters next to each other).
'in charge' becomes 'ic'.
'polite' with its last letter taken away is 'polit'.
'polit'+'ic'='POLITIC'
(Other definitions for politic that I've seen before include "Prudent, discreet" , "Sensible, judicious" , "Intriguing" , "Shrewdly tactful" , "Wise, cautious" .)