Word arranging another's letters (7)
I believe the answer is:
anagram
(Other definitions for anagram that I've seen before include "Word made by rearranging the letters of another" , "Gelding can be niggled by this" , ""Schoolmaster" is of "the classroom", for example" , "For racing tipster, starting price, for example" , "Word formed by rearranging another word" .)