When I was teaching, the word "separate" often gave kids a lot of spelling trouble. Which is why the little mnemonic saying "There's 'a rat' in separate" came in handy.

I don't know the single most commonly misspelled word. But I found this about the most common 100 words:
http://www.yourdictionary.com/library/misspelled.html
birdgirl73 Reviewed by birdgirl73 on . Which word In the English language is the most common misspelt word? Aww f*ck, this sucks. Sounded better in my head. I shall give it a go. Rating: 5