Lightning: That great electrical ZOT! that comes from the sky
They’re different words. Really, they are. I see many people who are otherwise decent spellers use lightening when they mean lightning. Why does this bug me so? I don’t know, but it does. Maybe it’s because I really like lightning storms.
Actually, the misspelling I see (and make) the most often is lightning/lighting. I once spent forty minutes stuck on a puzzle in one of the old Zork text-games because I kept leaving out that first “n” when trying to answer a riddle.
Heck, I once wasted a bunch of time playing the old adventure game Crypt of Medea because although I knew how to assemble a bomb, light it and run away, I kept forgetting to put the bomb down first.
I think part of the problem may be that in certain dialects of English (like mine) these two words are pronounced identically, so if one is typing in a great hurry one may put down the wrong word.