Gluey substance in wheat (6)
I believe the answer is:
gluten
'gluey substance in wheat' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for gluten that I've seen before include "Protein left after starch is removed from cereal grains" , "Protein in cereal grain" , "Gluey protein substance in flour" , "Sticky substance" , "Substance in cereals" .)