Small flash of light (5)
I believe the answer is:
glint
'small flash of light' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for glint that I've seen before include "Twinkle" , "Sparkle" , "Flash of light (in the eye?)" , "Glittering flash" , "Momentary flash of light" .)