female water spirit, 1821, from Modern Latin Undina (1650s), coined by Paracelsus ("De Nymphis") in his alchemical system, from Latin unda "a wave, billow" (see water (n.1)). Popularized by German romance "Undine, eine Erzählung" (1811) by Baron F.H.C. La Motte Fouqué. Undinism (1928) was coined by sex researcher Havelock Ellis to describe the fetish for urine (which Ellis had); nowadays it would be called urophilia.
