A gebbeth is the physical shell of a man or other being which has been consumed and possessed by another power.They feature in Ursula K. Le Guin's Earthsea series. These powers, referred to in the book as "the nameless ones" are beings remaining from the creation of "earthsea" where the books take place. In the book A Wizard of Earthsea, Ged summoned, and was pursued by one of these "nameless ones" and almost overpowered by it as a gebbeth in the form of Skiorh in Osskil. The series goes on for four books, and though the nameless ones show up again, the gebbeth is only mentioned.
The word 'Gebbeth' is used synonymously with 'instrument' in A Description of Earthsea.
The Enemy of Morred turned Elfarran's brother Salan into a gebbeth and used it to trick her into travelling to the Jaws of Enlad.