Blackish mole? (5)
I believe the answer is:
jetty
'mole?' is the definition.
(I know that breakwater can be written as jetty)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for jetty that I've seen before include "Quay" , "Dock" , "Pier - landing stage" , "Small landing stage" , "Wharf" .)