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fuller's earth full·er's earth (ful'ərz)
A highly absorbent claylike substance consisting of hydrated aluminum silicates, applied moistened with water as a poultice.
any fine-grained, naturally occurring earthy substance that has a substantial ability to adsorb impurities or colouring bodies from fats, grease, or oils. Its name originated with the textile industry, in which textile workers (or fullers) cleaned raw wool by kneading it in a mixture of water and fine earth that adsorbed oil, dirt, and other contaminants from the fibres.