Invoice company directors for large sign (9)
I believe the answer is:
billboard
'sign' is the definition.
(I know that billboard is a type of sign)
'invoice company directors for large' is the wordplay.
'invoice company' becomes 'bil' (I can't explain this - if you can you should give a lot more credence to this answer).
'directors' becomes 'board' (board of directors).
'for' means one lot of letters go next to another (I've seen this in other clues).
'large' becomes 'L' (eg in clothes sizes).
'board' after 'l' is 'lboard'.
'bil'+'lboard'='BILLBOARD'
Can you help me to learn more?
(Other definitions for billboard that I've seen before include "advertising space" , "Advertising hoarding" , "American hoarding" .)