nounScottish, British, Northern English
1dialect The eider, Somateria mollissima.
2dialect, rare Also "puffy dunter". Any of various cetaceans, especially the common porpoise, Phocoena phocoena, and Risso's dolphin, Grampus griseus.
Late 17th century; earliest use found in James Wallace (1642–1688), Church of Scotland minister and writer on Orkney. From dunt + -er, in each sense so called with reference to the plunging movements the animals make in the water.