Is corn a fruit, vegetable, or a nut?

Corn (Maize) is clearly a cereal grain, and not any of the other things you mention. Even the farmers and agricultural agencies consider it a grain - it's one of the "official grains of Canada" and regulated by the Canadian grain commission.

I'm not sure when or why it started being called a vegetable, but as far as the culinary definition goes, it has far too much sugar and starch to fall properly into that category. The typical culinary definition of a vegetable is savory, not sweet.

Botanically, the kernels can be considered a type of fruit called a caryopsis (AKA a grain), although it's not normally eaten as fruit (for one thing, it's normally cooked).

It may accompany vegetables reasonably well, just like rice or many other grains. But it is a grain.

In terms of culinary use, corn is either a grain or a vegetable. When we use it as cornmeal, polenta, or even popcorn, we're essentially thinking of it as a grain - and it really is a cereal grain. But when we eat sweet corn off the cob, or incorporated into a dish, we're thinking of it more as a vegetable. (It's still really a grain, but I think it's fair to say it's used as a vegetable sometimes.)

The kernel, the part we eat, is a seed.

Botanically, it is a grain. Its a giant grass. In most cuisines, it treated mostly as a starch.

The entire corn cob is a multiple fruit.

Corn kernels are seeds and the kernels is an ear. All the fruits of graminae are ears: this means "seed heads" made ??up of many fruits (usually insignificant) growing together, precisely in an ear. When the fruits are ripe ears of generating seeds.

In wheat, rice, rye grass, they are ears.

Oats are infructescenses

In corn are cobs:

All the fruits of true grasses are ears: this means "seed heads" made ??up of many fruits (usually insignificant) growing together, precisely in an ear. When the fruits are ripe ears of generating seeds.

There are many types of true grasse, some edible and some not. The visible ears are groups of seeds.

Same question you can ask for tomatoes or peppers = they are fruits, but used as vegetables.

Corn is a wildly diverse crop, human breeding has adapted it for many, many purposes:

• Cereal crop to be processed: You harvest the dried kernals of certain varieties of corn from the cob, and store them until they're ready to be processed and consumed, usually by soaking them in lye, then grinding them into a paste (masa) that is either used in recipes as is, or dried into cornmeal.

• Cereal crop to be stored and cooked: certain varieties of corn's kernels are exposed to heat, and their nutritious, starch laden meat is expanded into something that can be combined with water and other ingredients into a tasty gruel, or snacked on straight from the heat source (hot sand in pre-columbian cultures, animal or vegetable fats in colonial cultures, hot air in modern homes. Yup. Popcorn was an essential staple in some pre-columbian cultures.)

• Fresh vegetable/fruit: Sweetcorn is a perishable crop, who's caryopsis (kernels) have a sweet, moist texture very similar to fresh fruits and "vegetables" that are fruiting bodies of plants. While technically a whole grain, sweetcorn contains many vitamins and nutrients and flavor profiles associated with fresh produce.

A maize grain is considered a fruit because it shares some features with other fruits, for example: it has two scars, etc.