What an argument winner will have, being smart (3,4,4)
I believe the answer is:
the last word
I'm afraid I can't explain this answer.
Can you help me to learn more?
(Other definitions for the last word that I've seen before include "Finest example" , "This settles the argument" , "In Hamlet, shoot" , "Closing remark" , "it's the most up-to-date model" .)