Right side at sea (9)
I believe the answer is:
starboard
'right side at sea' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for starboard that I've seen before include "Right-hand side of ship while facing forward" , "Ship's right side" , "One side of a ship" , "right to 14 [YACHTS]" , "Sailor's right" .)