Cornfield flower (5)
I believe the answer is:
poppy
'cornfield flower' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for poppy that I've seen before include "Wild flower having its day in November" , "Cornfield flower" , "Flower of forgetfulness" , "Girl's name -- scarlet flower" , "Bright red flower, source of opium" .)