corn vs cereal grass

corn and cereal grass both are nouns.

Word	Noun	Adjective	Verb	Adverb
corn	Yes	No	Yes	No
cereal grass	Yes	No	No	No

As nouns, cereal grass is a hypernym of corn; that is, cereal grass is a word with a broader meaning than corn:

corn: tall annual cereal grass bearing kernels on large ears: widely cultivated in America in many varieties; the principal cereal in Mexico and Central and South America since pre-Columbian times
cereal grass: grass whose starchy grains are used as food: wheat, rice, rye, oats, maize, buckwheat, millet

Other hypernyms of corn include cereal.

As nouns, cereal grass is a hypernym of corn; that is, cereal grass is a word with a broader meaning than corn:

corn: (Great Britain) any of various cereal plants (especially the dominant crop of the region--wheat in Great Britain or oats in Scotland and Ireland)
cereal grass: grass whose starchy grains are used as food: wheat, rice, rye, oats, maize, buckwheat, millet

Other hypernyms of corn include cereal.

corn (noun)	cereal grass (noun)
something sentimental or trite	grass whose starchy grains are used as food: wheat, rice, rye, oats, maize, buckwheat, millet
ears of corn that can be prepared and served for human food
whiskey distilled from a mash of not less than 80 percent corn
tall annual cereal grass bearing kernels on large ears: widely cultivated in America in many varieties; the principal cereal in Mexico and Central and South America since pre-Columbian times
(Great Britain) any of various cereal plants (especially the dominant crop of the region--wheat in Great Britain or oats in Scotland and Ireland)
the dried grains or kernels or corn used as animal feed or ground for meal
a hard thickening of the skin (especially on the top or sides of the toes) caused by the pressure of ill-fitting shoes

corn (verb)	cereal grass (verb)
preserve with large-grained rock salt
feed (cattle) with corn