The Element Encyclopedia of Witchcraft: The Complete A-Z for the Entire Magical World - Judika Illes 2005
Solitary sidhe are not trooping fairies. Some perceive that they are a separate species of spirit, now lumped in with the sidhe. (And perhaps, in Gaelic, sidhe eventually became almost as generic as fairy in English.) Many are associated with death; some serve as psychopomps or death-knells.
The most famous is the bean-sidhe or banshee, which literally means “Fairy Woman” or “Woman of the Fairy Mound.” It is worthwhile to recall that “fairy mounds” are another name for the often treasure-filled barrows, ancient burial mounds that stud Europe and Asia (where they are known as kurgans).
In the Hollywood version of the banshee, hearing her voice causes death and so she has become a staple of horror entertainment. This is unfair: the banshee doesn’t kill or injure anyone nor does she scream for just anyone. She is a spirit who is attached to a specific family. (And it is a typically elegant family at that!)
She is the family’s personal escort to the realm of the dead. She does not kill but awaits death and mourns. Should a member of her family be about to die (for any reason; it could be a natural death of someone aged 102) she manifests herself and audibly keens, the traditional Celtic mourning wail. Obviously, however, she is a dreaded guest: her presence, usually both visible and audible, indicates imminent death and advises the family to begin making appropriate preparations.
The banshee manifests in various forms, including:
An old woman dressed in green with glowing red eyes in hollow sockets and long, wild, white hair
A deathly pale woman dressed in white with long, wild red hair
A beautiful woman, veiled in white
A shimmery, silvery woman with long, beautifully abundant silver-gray hair
A headless woman, naked from the waist up, often carrying a basin of blood
See DICTIONARY: Banshee.
Also among the solitary sidhe are the Leanhaun shee or “fairy lover.” This beautiful fairy haunts wells and springs in Ireland and the Isle of Man in search of human lovers. If they accept her love, they are doomed to be hers forever. She vampirically feeds off their life essence and so her lovers aren’t long-lived. However, there is some compensation: she infuses them with tremendous poetic and literary skills. The Leanhaun shee is blamed for the brief lives of many of Ireland’s greatest poets but credited with bestowing their talent.