Shower reportedly sit on the throne (5)
I believe the answer is:
reign
'sit on the throne' is the definition.
(reign as a monarch)
'shower reportedly' is the wordplay.
'shower' becomes 'rain' (rainfall).
'reportedly' shows a homophone (sound like).
'rain' sounds like 'REIGN'.
(Other definitions for reign that I've seen before include "Dominion" , "Predominance" , "Period of monarch" , "Monarch's rule" , "Rule of monarch" .)