In the European magical lore an Undine is an elemental creature spirt of the water. The name was first used by the Swiss metaphysician Paracelsus in the early 16th century, the name derived from the Latin undas (wave). Undine is invoked in magical working requiring the cooperation of the waters. The leader of the Undines are called Necksa.
John and Caitlin Matthews, The Element Encyclopaedia of Magical Creatures, 2013, Undine, p 487