Bill when Charles will reign? (6)
I believe the answer is:
poster
'bill' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for poster that I've seen before include "Large decorative printed picture" , "Large sheet of paper advertising something" , "'Notice, placard (6)'" , "Printed advert" , "Large advert" .)