Reportedly the most important US state (5)
I believe the answer is:
maine
'us state' is the definition.
(I've seen this before)
'reportedly the most important' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'the most important' becomes 'main' (I've seen this before).
'main' sounds like 'MAINE'.
(Other definitions for maine that I've seen before include "The USA's Pine Tree State" , "state of USA" , "New England state" , "Part of America" , "NE US state" .)