Merriam-Webster Collegiate Dictionary - anagram

 I. noun  Etymology: probably from Middle French ~me, from New Latin ~mat-, ~ma, modification of Greek ~matismos, from ~matizein to transpose letters, from ana- + grammat-, gramma letter — more at gram  Date: 1589  1. a word or phrase made by transposing the letters of another word or phrase  2. plural but singular in construction a game in which words are formed by rearranging the letters of other words or by arranging letters taken (as from a stock of cards or blocks) at random  • ~matic also ~matical adjective  • ~matically adverb  II. transitive verb  (-grammed; -gramming)  Date: 1630  1. ~matize  2. to rearrange (the letters of a text) in order to discover a hidden message