Shrill insect (6)
I believe the answer is:
cicada
'shrill insect' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cicada that I've seen before include "Chirpy type" , "Large bug" , "Insect, produces high-pitched drone" , "Noisy tropical insect" , "Shrill insect" .)