Overly quick (5)
I believe the answer is:
hasty
'overly quick' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hasty that I've seen before include "Impulsive" , "Rushed; rash" , "Quick but ill-considered" , "Too hurried, careless" , "Impetuous - quick-tempered" .)