River in New England state on the sea (6)
I believe the answer is:
marine
'the sea' is the definition.
(thesaurus)
'river in new england state' is the wordplay.
'river' becomes 'r'.
'in' is an insertion indicator.
'new england state' becomes 'maine' (I've seen this before).
'r' placed into 'maine' is 'MARINE'.
'on' acts as a link.
(Other definitions for marine that I've seen before include "Member of the forces" , "Concerning the sea" , "Soldier-sailor" , "Airmen (anag.)" , "jolly" .)