Gentleman's address father cut short (3)
I believe the answer is:
sir
'gentleman's address' is the definition.
(I've seen this before)
'father cut short' is the wordplay.
'father' becomes 'sire' (synonyms).
'cut short' means to remove the last letter.
'sire' with its final letter removed is 'SIR'.
(Other definitions for sir that I've seen before include "Knight's title" , "Noble title of undesirable kind" , "Gentleman's form of address" , "Title for knight or teacher" , "Honorary male title" .)