The man’s greeting son (3)
I believe the answer is:
his
'the man's greeting son' is the definition.
I can't judge whether this defines the answer.
'greeting son' is the wordplay.
'greeting' becomes 'hi' (hi is a kind of greeting).
'son' becomes 's' (genealogical abbreviation for son).
'hi'+'s'='HIS'
Can you help me to learn more?
(Other definitions for his that I've seen before include "Belonging to that man" , "that chap's" , "Belonging to the male" , "It belongs to him" , "To - Coy Mistress (Marvell)" .)