cereal vs food grain

cereal and food grain both are nouns.

Word	Noun	Adjective	Verb	Adverb
cereal	Yes	Yes	No	No
food grain	Yes	No	No	No

As nouns, cereal and food grain are synonyms defined as:

cereal and food grain: foodstuff prepared from the starchy grains of cereal grasses

Other synonyms of cereal include grain.

cereal (noun)	food grain (noun)
a breakfast food prepared from grain	foodstuff prepared from the starchy grains of cereal grasses
foodstuff prepared from the starchy grains of cereal grasses
grass whose starchy grains are used as food: wheat, rice, rye, oats, maize, buckwheat, millet

cereal (adjective)	food grain (adjective)
made of grain or relating to grain or the plants that produce it