North European sea (6)
I believe the answer is:
baltic
'north european sea' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for baltic that I've seen before include "N European sea" , "The Sea around Scandinavia" , "Nearly land-locked sea of Scandinavia" , "Near-landlocked sea of N Europe" , "Coming from Tallinn, perhaps" .)