Stand in (for) (8)
I believe the answer is:
deputise
'stand in for' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for deputise that I've seen before include "Stand in for" , "Appoint as a substitute" , "Appoint as representative" , "Appoint as stand-in" , "Act as delegate for a person" .)