It's very smart. You can't say more than that (4,4)
I believe the answer is:
last word
But I can't explain it at all! Could you help me understand?
(Other definitions for last word that I've seen before include "Final statement in dispute, often decisive" , "It's state-of-the-art" , "Dernier cri" , "Most up-to-date - final decision" , "Final remark in argument" .)