It's "helvete", the "-vete" part of which comes from "veti", the Old Norse word for "punishment", according to Wiktionary. The word literally means "Hel's punishment", Hel being the ruler of the death realm in Norse mythology, Niefelheim. So the word does not originally refer to the Christian hell, though the English word seems to be related, I'd guess because of the Viking attacks on England.
The word "vete" is, once again according to Wiktionary, derived from the Old Norse hveiti, which comes from the Proto-Germanic word for "white", so I'm pretty sure there's no relation. Also, "vete" means "wheat", not "corn". "Corn" is "majs".
Tack så mycket! I really appreciate your explanation. Just a little detail regarding "corn". This word also means "wheat" in England. For example, in Shakespeare's King Lear Act IV, scene IV: "Darnel, and all the idle weeds that grow / In our sustaining corn. A century send forth".
Adolf Fredrik, more likely: https://en.wikipedia.org/wiki/Adolf_Frederick,_King_of_Sweden#Death
It does mean that, but they're not interchangeable – till döds would sound like really bad Swedish here, slå ihjäl is the set combination with slå.
till döds is used a lot with abstract nouns, like Kärlek till döds 'love to the death'. It can also be used with verbs, especially when death would not be a necessary consequence of that verb, for instance blev misshandlad till döds 'was beaten to death' (can't think of a better verb for misshandla atm)
ihjäl is a particle that only works together with verbs. If you use it in perifrastic passive forms, it should go at the start of the verb: blev ihjälslagen.