They're used by scriptwriters (7)
I believe the answer is:
letters
'scriptwriters' is the definition.
Although both the answer and definition are plural nouns, I can't understand how one could define the other.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for letters that I've seen before include "They are bound to look after tenants" , "Written notes" , "They may indicate a degree" , "Literary culture" , "A, B, C, D etc" .)