cereal

Where it comes from

Cereal ordinarily means grain grown for food, or a breakfast food made from grain. Cereal comes from Latin cerealis, meaning of grain and originally of Ceres. Ceres was the Roman goddess of agriculture and grain crops. English first used cereal as an adjective for grain-producing plants, then as a noun for those plants and their grain.

How the meaning developed

Only later did the noun narrow in everyday use to prepared grain food, especially the boxed breakfast familiar today.

In use

One belongs in a bowl. The other happens in a series.
Which spelling fits: I ate ______ for breakfast?

“Cereal” is a grain food.
“Serial” means happening in a series, or a story told in parts.
Your breakfast does not need a season finale.