> Tun frere n’ad ne pain ne ble ne vin
> ‘Your brother has neither bread nor corn nor wine;
nope: ble is wheat in modern French, and corn had not been brought back from the new world yet when this poem was written.
This usage surives in "corned beef", which refers to granular salt used for preserving the meat, nothing to do with cereal grains.
"Corn" still refers to multiple cereals in British English; what Americans call "corn" is "maize". Or so it used to be; perhaps it is changing?
"Corn" also refers to a lump of hardened skin; but that has a different origin, related to "horn", going back to Greek. It shares with "cornucopia" and "cornet" and "keratin".
"acorn" is also not derived from "corn", interestingly; it has its own etymology. It is not a portmanteau of "aiken corn" (oak tree's corn) or anything like that as might be wrongly guessed.
"kernel" is related to "corn" though, not to horns or keratin. OS kernels are named because they are the central part, like a seed, not because kernel programmers have thick skins or devil horns.
In the UK, there are some exceptions, where it specifically refers to maize: cornflakes, corn on the cob, sweetcorn, and cornflour.
Otherwise 'sweetcorn' or 'corn on the cob' ('corncob') are common. But you can't have e.g. 'wheat on the cob' so it's not ambiguous.
May be you can find reference to corn in Chaucer, I don't exactly remember if it is there for sure.