Archdeacon in time to repay (6)
I believe the answer is:
avenge
'to repay' is the definition.
(I've seen this before)
'archdeacon in time' is the wordplay.
'archdeacon' becomes 'ven' (abbreviation for The Venerable).
'in' means one lot of letters goes inside another.
'time' becomes 'age' (an age is a period of time).
'ven' placed into 'age' is 'AVENGE'.
(Other definitions for avenge that I've seen before include "Gain retribution" , "Take satisfaction for injury or wrong" , "Geneva (anag)" , "Exact retribution, take satisfaction for injury" , "Pay back for" .)