Eg, rye (6)
I believe the answer is:
cereal
'eg rye' is the definition.
(rye is a kind of cereal)
This is all the clue.
(Other definitions for cereal that I've seen before include "Grass cultivated for food" , "Breakfast food made from grain" , "Rye, for example" , "Maize, rye or the like" , "Breakfast dish" .)