Place to tie up a boat (4)
I believe the answer is:
pier
'place to tie up a boat' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pier that I've seen before include "Ripe as a jetty (4)" , "Bridge pillar" , "Building projecting into the sea" , "seaside building" , "such as you might see at the seaside" .)