Second Monopoly avenue (6)
I believe the answer is:
baltic
'second monopoly avenue' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for baltic that I've seen before include "Coming from Tallinn, perhaps" , "Sea of northern Europe" , "Northern European sea" , "The Sea around Scandinavia" , "Almost land-locked sea of NE Europe" .)