Not used to good advantage (6)
I believe the answer is:
wasted
'not used to good advantage' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for wasted that I've seen before include "Squandered or withered" , "Squandered or weakened" , "Frittered away" , "Spent unprofitably - emaciated" , "Dissipated; atrophied" .)