The gentleman didn’t allow father to finish (3)
I believe the answer is:
sir
'the gentleman' is the definition.
(a man may be addressed as sir)
'didn't allow father to finish' is the wordplay.
'didn't allow' becomes 'si' (I can't explain this - if you can you should give a lot more credence to this answer).
'to finish' suggests the final letters.
The last letter of 'father' is 'r'.
'si'+'r'='SIR'
Can you help me to learn more?
(Other definitions for sir that I've seen before include "Knight's title" , "address to teacher" , "Poet and novelist" , "Way to address gentleman" , "Term of address for a gentleman" .)