Outstanding coastal feature (4)
I believe the answer is:
pier
'outstanding coastal feature' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
This is all the clue.
Can you help me to learn more?
(Other definitions for pier that I've seen before include "Building projecting into the sea" , "Buttress; landing place" , "Break-water or landing stage" , "Seaside structure" , "Platform built out from the shore, supported on piles" .)