"one who fulls cloth," Old English fullere, from Latin fullo "fuller" (see foil (v.)). The substance called fuller's earth (silicate of alumina) is first recorded 1520s, so called because it was used in cleansing cloth.
The word "full" is from the Anglo-Saxon fullian, meaning "to whiten." To full is to press or scour cloth in a mill. This art is one of great antiquity. Mention is made of "fuller's soap" (Mal. 3:2), and of "the fuller's field" (2 Kings 18:17). At his transfiguration our Lord's rainment is said to have been white "so as no fuller on earth could white them" (Mark 9:3). En-rogel (q.v.), meaning literally "foot-fountain," has been interpreted as the "fuller's fountain," because there the fullers trod the cloth with their feet.