Flashing light (6)
I believe the answer is:
strobe
'flashing light' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for strobe that I've seen before include "Light that seems to spin" , "High-intensity flashing beam of light" , "Flasher" , "something flashy" , "Flashing-light device" .)