Why is the ninth month called September?
1650s, from Modern Latin sylphes (plural), coined 16c. by Paracelsus (1493-1541), originally referring to any race of spirits inhabiting the air, described as being mortal but lacking a soul. Paracelsus' word seems to be an arbitrary coinage, but perhaps it holds a suggestion of Latin sylva and Greek nymph. The meaning "slender, graceful girl" first recorded 1838, on the notion of "light, airy movements." Silphid (1670s) are the younger or smaller variety, from French sylphide (1670s).
an imaginary or elemental being that inhabits the air and is mortal but soulless. The existence of such beings was first postulated by the medieval physician Paracelsus, who associated a different being with each of the four elements (earth, air, fire, and water). Compare gnome; undine.