I once taught a class in which I explained to the students the concepts of "premise" and "conclusion," but I neglected to write the word "premise" on the blackboard.
Later, a student in the class submitted a paper that made reference to someone's "primus." I looked the word up in the dictionary and learned that, besides being the name of a brand of stove, it signified a kind of bishop in the Church of Scotland, which didn't seem to fit the context.
Eventually I figured out that the student meant "premise," that she was guessing at the spelling according to how she had heard it, and that she thought it rhymed with "grimace." I guess it does if you're from the South.