Grammar Cop has cited writers in the past for using words that aren’t words. Irregardless is one. Reoccur is another. Neither is a real word, but writers use them instead of regardless and recur. 

Here’s another. Unthaw. The word is  thaw.  Unthaw isn’t a real word, but if it were it would be a synonym for freeze. 

Watch out for those pesky non-words. When in doubt, check a reliable dictionary.