Flicker (5)
I believe the answer is:
waver
'flicker' is the definition.
(I know that flicker can be written as waver)
This is all the clue.
(Other definitions for waver that I've seen before include "Show hesitation, begin to give way" , "Be irresolute; flicker" , "Not be sure of" , "fluctuate" , "Vacillate" .)