From The Art and Popular Culture Encyclopedia
Ondines or undinesare elementals, enumerated as the water elementals in works of alchemy by Paracelsus. They also appear in European folklore as fairy-like creatures; the name may be used interchangeably with those of other water spirits. Undines were said to be able to gain a soul by marrying a human and bearing his child.
Undine A water nymph without a soul, which she later received by marrying a mortal and bearing a child: Heroine of a book (1812) by Baron Friedrich de la Motte Fouqué, German author