Lead-in to an alias (3)
I believe the answer is:
aka
'lead-in to an alias' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aka that I've seen before include "Notation with initials indicating alternative name" , "Notation indicating alias or other name" , "Also called (abbrev.)" , "Using the byline" , "Notation indicating alternative identity" .)