What a possessive father calls his son? (2,3)

I believe the answer is:

my boy

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'what a possessive father calls' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'his son?' is the wordplay.
'his' becomes 'my' (I can't explain this - if you can you should believe this answer much more).
'son?' becomes 'boy' ('boy' can be a synonym of 'son').
'my'+'boy'='MY BOY'

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