Secure reversal of roles (5)
I believe the answer is:
strap
'secure' is the definition.
(I know that strap is a type of secure)
'reversal of roles' is the wordplay.
'reversal of' says the letters should be written backwards.
'roles' becomes 'parts' ('part' can be a synonym of 'role').
'parts' written backwards gives 'STRAP'.
(Other definitions for strap that I've seen before include "Restraining fastener" , "Shoulder band" , "Beat; securing band" , "Fasten; punishment" , "Leather fastener" .)