WordNet sense 1 (a cluster of seven stars in Ursa Minor; at the end of the dipper's handle is Polaris):

Little Dipper

WordNet sense 2 (a group of seven bright stars in the constellation Ursa Major):

plough, wagon, wain, Big Dipper, Charles's Wain

WordNet sense 3 (small North American diving duck; males have bushy head plumage):

butterball, bufflehead, Bucephela albeola

WordNet sense 4 (small stocky diving bird without webbed feet; frequents fast-flowing streams and feeds along the bottom):

water ouzel