Principal-sounding state (5)
I believe the answer is:
maine
'state' is the definition.
(US state)
'principal-sounding' is the wordplay.
'principal' becomes 'main' (both can mean major).
'sounding' becomes 'e' (I've seen this in other clues).
'main'+'e'='MAINE'
(Other definitions for maine that I've seen before include "somewhere in America" , "American state, capital Augusta" , "state of USA" , "NE US state" , "Part of America" .)