The father I aim to make an ally of (6)
I believe the answer is:
friend
'make an ally of' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'the father i aim' is the wordplay.
'the father' becomes 'fr' (abbreviation as in a priest's title).
'aim' becomes 'end' (both can mean a goal or purpose).
'fr'+'i'+'end'='FRIEND'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for friend that I've seen before include "One who gives proof of genuine regard" , "One you know well and regard with affection" , "Close associate" , "Ally, supporter" , "China" .)