Not exactly an eponym, but Paracelsus is given credit for coining the word "sylph"
though present meaning is not what he gave it, apparently.

sylph - 1657, from Mod.L. sylphes (pl.), coined 16c. by
Paracelsus, originally referring to any race of spirits
inhabiting the air, described as being mortal but lacking a
soul. The meaning "slender, graceful girl" first recorded
1838, on the notion of "light, airy movements."