Main marker (4)
I believe the answer is:
buoy
(Other definitions for buoy that I've seen before include "Floating item often marking a hazard" , "Warning float" , "Floating navigation mark" , "Warning floater" , "Floating guide marker" .)
I believe the answer is:
buoy
(Other definitions for buoy that I've seen before include "Floating item often marking a hazard" , "Warning float" , "Floating navigation mark" , "Warning floater" , "Floating guide marker" .)