Copper symbolically said farewell (3,3)
I believe the answer is:
see you
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for see you that I've seen before include "For so long" , "Later we'll meet" , "Informal kind of au revoir - with visual intent" , "poker-playing expression?" , "Casual and informal goodbye" .)