Jetty (4)
'jetty' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for pier that I've seen before include "Structure extending seawards" , "Wharf jutting out into water" , "Quay" , "such as you might see at the seaside" , "Seaside resort feature" .)
(Other definitions for mole that I've seen before include "Small congenital skin spot" , "Groyne" , "spy a > breakwater" , "Small spot - small mammal" , "Breakwater; naevus" .)