Chafe or fray (3)
I believe the answer is:
I believe this is a double definition.
'chafe' is the first definition.
(I know that chafe can be written as rub)
'fray' is the second definition.
(I know that fray can be written as rub)
(Other definitions for rub that I've seen before include "Ointment; copy (a brass)" , "Remove marks - ... out" , "Cause friction" , "Massage or buff" , "Apply friction to - difficulty" .)