Homonym Hump Day - Lightning or Lightening?

[chrissymunder]

I can remember going back and forth on this one when I wrote Start from the Beginning and the storm blew in off the lake. There's a big difference between a flash of electrical discharge and lessening someone's burden. Still, I kept wanting to stick that "e" in there. Do you have a pet word that even though you know the difference between them you confuse the spelling?