Cove or bay (5)
I believe the answer is:
inlet
This clue is a double definition.
'cove' is the first definition.
(synonyms)
'bay' is the second definition.
(I've seen this before)
(Other definitions for inlet that I've seen before include "Entry port" , "Opening through which fluid can pass" , "bit of a lake here?" , "Small area of sea" , "Arm of lake, river" .)