Jetties are structures built in waterways to protect shorelines from erosion and to provide a safe harbor for boats. Piers, which are five letter words, are structures that extend out into the water and are used to moor boats. Moles, also five letter words, are similar to piers but are built on land and extend out into the water. Seawalls, eight letter words, are structures built along the shoreline to protect it from erosion and flooding. All of these structures are examples of jetties.