Rule for shower, we hear (5)
I believe the answer is:
reign
'rule' is the definition.
(I know that reign is a type of rule)
'shower we hear' is the wordplay.
'shower' becomes 'rain' (rainfall).
'we hear' shows a homophone (sound like).
'rain' is a homophone of 'REIGN'.
'for' is the link.
(Other definitions for reign that I've seen before include "Predominance" , "Control" , "Monarch's period" , "Hegemony" , "Time on throne" .)