Cornfield cry (3)
I believe the answer is:
caw
'cornfield cry' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for caw that I've seen before include "Call like rook" , "Crow's call" , "Sound made by a crow, say" , "Rook's cry" , "Rook's call" .)