Flung niece out with no good effect (9)
I believe the answer is:
influence
'effect' is the definition.
(I know that influence is a type of effect)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for influence that I've seen before include "Sway, dominance" , "Clue in fen (anag.)" , "Power to affect persons or events" , "The capacity to affect others" , "Weight" .)