noun
A structure extending into the sea to protect a harbor or serve as a landing place. Often used in civil engineering and maritime contexts.
港の入り口に長い突堤が伸びている。
A long jetty extends at the entrance of the harbor.
突堤の先端に灯台が立っている。
A lighthouse stands at the tip of the breakwater.
Compound of 突 (thrust, protrude) and 堤 (embankment, dike). The kanji directly suggest a protruding embankment.