The intonation with which no gentleman finishes a sentence? (7)
I believe the answer is:
cadence
'the intonation' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'no gentleman finishes a sentence?' is the wordplay.
'no gentleman' becomes 'cad' (I've seen this in another clue).
'finishes a sentence?' becomes 'ence' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'cad'+'ence'='CADENCE'
'with which' is the link.
Can you help me to learn more?
(Other definitions for cadence that I've seen before include "Close of a musical phrase" , "Closing bars" , "that may be perfect for musicians" , "Lilt" , "Rhythm of the voice" .)