Feth is the name of the supernatural spirit that is believed to possess the nal-wood trees on the planet Tanith, allowing them to move their position. The troops of the Imperial Guard regiment known as the Tanith 1st ("Tanith First-And-Only"), which is comprised of the only surviving natives of Tanith, use it as an expletive. After Gaunt's Ghosts are stationed at Vervunhive, it is combined with the native word "gak" to form such expressions as "fething gakhead."