The gentleman father cut short (3)
I believe the answer is:
sir
'the gentleman' is the definition.
(I've seen this before)
'father cut short' is the wordplay.
'father' becomes 'sire' ('sire' can be a synonym of 'father').
'cut short' means to remove the last letter.
'sire' with its last letter taken off is 'SIR'.
(Other definitions for sir that I've seen before include "Title of knight or baronet" , "Term of address for a gentleman" , "Gentleman's form of address" , "Baronet's title" , "Male form of address" .)