Muss (6)
I believe the answer is:
rumple
'muss' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rumple that I've seen before include "Wrinkle, make uneven" , "Make dishevelled" , "Make untidy, say clothes" , "Wrinkle, fold or crease" , "Make uneven or wrinkled" .)