Just leading characters, to start with (9)
I believe the answer is:
initially
'with' is the definition.
Both the answer and definition are adverbs. Maybe there's an association between them I don't understand?
'just leading characters to start' is the wordplay.
'just leading characters' becomes 'ly' (I can't explain this - if you can you should give a lot more credence to this answer).
'to' says to put letters next to each other (I've seen this in other clues).
'start' becomes 'initial' (I have seen 'Start of name' mean 'initial' so perhaps 'start' could also mean 'initial').
'ly' after 'initial' is 'INITIALLY'.
Can you help me to learn more?
(Other definitions for initially that I've seen before include "How laser, for example, was put together" , "Firstly" , "At the start" , "At first" , "In the beginning" .)