Tell me about the word corn. It seems that in European English it means grain. How does that relate to the New World product called by Americans corn? What do people in the UK call corn on the cob?
Was corn just a word for grain that was later applied to the American English corn? What do Canadians call it?
How does the terminology work in European vs. New world Spanish?
Maize.
US/CA/AU/NZ are corn, according to here.
Corn is, or was at least, indeed the general term for grain. This is the origin of acorn, for instance.
What we now call corn was so ubiquitous in the Americas that the general became the particular, in the same way that some Americans call all soda “coke”.
The particular word for that grain is, or at least was, maize.
There’s also peppercorn, barleycorn and corned beef which is cured with corns of salt.
Maíz is maíz, regardless of which side of the Atlantic you’re on.
As Cecil says, “corn” generally refers to whichever grain crop is most common in a particular region, which, in the USA (but few other places) is generally maize. In Britain, corn on the cob, sweetcorn, and popcorn are called “corn on the cob”, “sweetcorn”, and “popcorn”, but the corn growing out in the farmer’s field is generally wheat. Sometimes the grain in the farmer’s field may be oats or barley, and if so, they will generally be called that, rather than “corn”.
Really, the only people who seem to get at all confused or bothered by this are chauvinistic Americans who want to insist that “corn” must always and everywhere only be used to mean maize.
Yup. “Corn” doesn’t just cover cereal grains; it covers any kind of grains at all, including grains of salt or sand, though that usage is probably obsolete now. But it survives in “corned beef”, which has been treated with granular salt.
Corn on the cob.
When the kernels are served off the cob, we call it sweetcorn.
The field itself will often be called a cornfield though.
Incidentally, in German, “Korn” means a single grain of anything (or, in a pars pro toto way, a lot of it).
And “cornflour” in the UK is corn starch, that is, maize flour - never wheat flour.
Also related to kernel. There also seems to be a relation between grain and gram.
Also, cereals (chiefly wheat, barley, oats, rye - and not so often, maize) are sometimes referred to collectively as ‘corn crops’.
If there is, it’s a fairly distant relationship. Gram/gramme, in the sense of the unit of weight, comes to English, through French, from Latin and ultimately from Greek gramma, a small weight. Whereas grain comes from the Latin granum, meaning a single grain (of anything).
Of course it’s possible that the Greek small weight and the Latin single grain share a common Indo-European root. But it’s equally possible that “corn” shares the same root - a word with a “ger”-stem meaning something worn down or wasted away.
In Norwegian “korn” is pretty much used everywhere English uses grain. (Except for when it isn’t.) But Swedish, for some reason, has decided the proper cereal crop, the one that gets to be called “korn”, is Barley. Korn – Wikipedia
It all sounds pretty corny to me:)
I’ve generally understood “corn” (in the more general European-style usage) to refer to any grain that typically grows with many kernels together in a compact head.
See this photo. The left two stalks (barley and wheat) might be called corn. The stalk on the right (oats) would probably not be called corn. At least, that’s how I’ve thought the word is used.
In America, “corn” refers almost exclusively to maize in particular. It’s rarely called by the name “maize”. It’s usually just called corn. Although, I think “maize” is sufficiently well-known that most everyone in America understands that too.
It’s popular around Thanksgiving time for corn farmers to plow a maze (get it?) into their corn fields, like this one, which is always popular with kids. Advertising for such mazes commonly involves punny plays on “maze”, “maize”, and “amazing”. I think that’s how most Americans come to know the word “maize” 
Midwesterners you mean. I’ll say “semi-widespread” beyond that.
Old commercial: Maize: You Call it Corn (youtube). But I thought it was (scanning Wikipedia for any Native American languages I actually know the name for)… they call it Naadą́ą́ʼ in the biggest native US language.
It’s actually Taíno via Spanish, but they aren’t even mainlanders.
This is also common in the UK as well - at least in the southwest, where there are 5 or 6 maize mazes that I drive past relatively regularly when they are in season. Such as this one.
I don’t think they are as large as the ones in your link though!
Just for the record, “corn” is used to mean maize in Canada as well. In French Canada, there are two words: “maïs” but also “blé dinde”, literally “Indian corn”, although the word “blé” unadorned means wheat. I assume that the original American word was “Indian corn”, which then got shortened to “corn”. Remember that corn was a new world product and would have been new to the colonials.
