Dossier letters (3)
I believe the answer is:
aka
'dossier letters' 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 "Notation indicating alternative identity" , "Notation with initials indicating alternative name" , "Also known as, initially" , "Also called (abbrev.)" , "Notation indicating alias or other name" .)