New in: silver dollar that is back as part of the service (5,3)
I believe the answer is:
agnus dei
'part of the service' is the definition.
'agnus dei' can be an answer for 'part' (I have seen 'part of mass' mean 'agnus dei' so perhaps 'part' could also mean 'agnus dei'). I am not sure about the 'of the service' bit.
'new in silver dollar that is back' is the wordplay.
'new' becomes 'n'.
'in' indicates putting letters inside.
'silver' becomes 'ag' (Ag is the chemical symbol for silver).
'dollar' becomes 'us' (US dollar is an example).
'that is back' becomes 'dei' (I can't explain this - if you can you should believe this answer much more).
'ag'+'us'='agus'
'n' inserted into 'agus' is 'agnus'.
'agnus'+'dei'='AGNUS DEI'
'as' is the link.
Can you help me to learn more?
(Other definitions for agnus dei that I've seen before include "sacrificial offering" , "'Latin mass prayer, Lamb of God (5,3)'" , "Emblem of Christ" , "part in requiem" , "Part of Latin Mass" .)