I have something that pops up when a word is misspelled and asked if I want the spellchecker to add and remember it, occasionally I accidentally hit yes, then it will suggest that or auto correct it to that misspelled word. I have yet to fig out how to delete the misspelled words.
You are on Android right?
Setting, apps, keyboard, clear data. Note that this will also reset any keyboard preferences that you have saved.
(I am using a VERY old version of android so things may have changed a bit but I think it works more or less the same way. Also the keyboard might be called something like "android keyboard" instead of "keyboard" -- I'm sure you can find it)