Burn unsteadily (7)
I believe the answer is:
flicker
'burn unsteadily' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for flicker that I've seen before include "Twinkle" , "Shine unsteadily; waver" , "Vary rapidly in brightness" , "Burn or shine unsteadily" , "Woodpecker" .)