Principal part of New England, it's said (4)
I believe the answer is:
main
'principal' is the definition.
(both can mean major)
'part of new england it's said' is the wordplay.
'part of new england' becomes 'Maine' (state in the New England region).
'it's said' indicates a 'sounds like' (homophone) clue.
'maine' is a homophone of 'MAIN'.
(Other definitions for main that I've seen before include "(The mighty) sea" , "Principal or high seas" , "Cardinal" , "Most important or greatest in size" , "Chief, primary" .)