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