I've noticed a common misspelling: Rediculous. I think I know why. It's our pronunciation. We say it as though it has the prefix "re" and as such try to spell it that way. It looks ridiculous. I used to make the same mistake until I realised the cause of my error. It's RIDiculous not REdiculous. It's like ridicule.
"Ah ha!" said I. "I know how to spell ridicule."
Etymology wins again. All is well. Hooray.