Roles reversed in tie (5)
I believe the answer is:
strap
'tie' is the definition.
(I've seen this before)
'roles reversed' is the wordplay.
'roles' becomes 'parts' ('part' can be a synonym of 'role').
'reversed' shows that the letters should be reversed in order.
'parts' in reverse letter order is 'STRAP'.
'in' acts as a link.
(Other definitions for strap that I've seen before include "Leather fastening" , "Leather fastener" , "Tie" , "something to hang on to" , "loopy band" .)