Power drops, it's said (5)
I believe the answer is:
reign
'power' is the definition.
(reign can mean time in power)
'drops it's said' is the wordplay.
'drops' becomes 'rain' (drops of water).
'it's said' indicates a 'sounds like' (homophone) clue.
'rain' sounds like 'REIGN'.
(Other definitions for reign that I've seen before include "Rule of monarch" , "time in power" , "Prevail" , "period in power" , "Time on throne" .)