Undermined book in deed (6)
I believe the answer is:
dented
'undermined' is the definition.
The answer and definition can be both to do with contact as well as being past participle verbs.
Maybe there's an association between them I don't understand?
'book in deed' is the wordplay.
'book' becomes 'nt' (New Testament).
'in' indicates putting letters inside.
'nt' placed into 'deed' is 'DENTED'.
Can you help me to learn more?
(Other definitions for dented that I've seen before include "Made small depression in metal surface" , "Made depression in through pressure or impact" , "made an impression" , "Tended to be depresed" , "Dinged" .)