Give a nickname to (3)
I believe the answer is:
'give a nickname to' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dub that I've seen before include "Give nickname, knighthood, to" , "Knight (someone) with a sword" , "Label, name" , "Add sound effects or music" , "Raise to knighthood" .)