The Element Encyclopedia of Witchcraft: The Complete A-Z for the Entire Magical World - Judika Illes 2005
This Scottish word literally indicates “old woman” or “hag” but may have once been the name or title for the presiding spirit of Samhain, the Celtic festival corresponding with November Eve or Halloween. Some perceive this as the title for the witch-goddess Nicnevin in her Hag aspect.
The ancient Celtic calendar was divided into two halves, light and dark. Samhain marks the beginning of the dark half of the year, which ended six months later at Beltane. The Carlin, an aged Frost Queen, ruled this part of the year until she was superceded in the spring by the beautiful May Queen or Beltane Bride.
Traditionally, displaying the last reaped sheaf of grain (the Carlin or Cailleach) on Samhain indicated that the appropriate rituals had been followed. Displaying this sheaf kept a household safe from malicious spirits who might be out and about on that night.
See Beltane Carline, Gyre Carlin; CALENDAR: Beltane, Halloween, Samhain, Walpurgis; DIVINE WITCH: Befana, Mana, Nicnevin.