The word murder spelled backwards. It was first used in "The Shining" by Stephen King and then in both the film and the miniseries that were made based on the book.
Sam: Anagram, maybe?
Dean: I think it's an anagram.
Kraus: A what?
Dean: An anagram. Same letters, different words.
Dean: You know, it's, uh, maybe word fragments... other times, it's anagrams.