WordNet sense 1 (a motorboat resembling a motor scooter):

water scooter, sea scooter

WordNet sense 2 (a wheeled vehicle with small wheels and a low-powered gasoline engine geared to the rear wheel):

motor scooter

WordNet sense 3 (a sailing vessel with runners and a cross-shaped frame; suitable for traveling over ice):

iceboat, ice yacht

WordNet sense 4 (large black diving duck of northern parts of the northern hemisphere):

scoter