Nocturnal insect (4)
I believe the answer is:
moth
'nocturnal insect' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for moth that I've seen before include "Night flier" , "Nocturnal winged insect" , "Night-flying insect" , "Insect attracted to light" , "Night-flier" .)