Lightning flash? (6)
I believe the answer is:
streak
I believe this is a double definition.
'lightning' is the first definition.
(thesaurus)
'flash?' is the second definition.
(I know that streak is a type of flash)
(Other definitions for streak that I've seen before include "One may be lucky" , "run out of gear" , "Run naked in a public place" , "Run unclothed" , "exposz" .)