cereal vs oat

cereal and oat both are nouns.

Word	Noun	Adjective	Verb	Adverb
cereal	Yes	Yes	No	No
oat	Yes	No	No	No

As nouns, oat is a hyponym of cereal; that is, oat is a word with a more specific, narrower meaning than cereal:

cereal: foodstuff prepared from the starchy grains of cereal grasses
oat: seed of the annual grass Avena sativa (spoken of primarily in the plural as `oats')

As nouns, oat is a hyponym of cereal; that is, oat is a word with a more specific, narrower meaning than cereal:

cereal: grass whose starchy grains are used as food: wheat, rice, rye, oats, maize, buckwheat, millet
oat: annual grass of Europe and North Africa; grains used as food and fodder (referred to primarily in the plural: `oats')

cereal (noun)	oat (noun)
a breakfast food prepared from grain	seed of the annual grass Avena sativa (spoken of primarily in the plural as `oats')
foodstuff prepared from the starchy grains of cereal grasses	annual grass of Europe and North Africa; grains used as food and fodder (referred to primarily in the plural: `oats')
grass whose starchy grains are used as food: wheat, rice, rye, oats, maize, buckwheat, millet

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