fuller's earth

• IPA^(key): /ˌfʊləz ˈɜːθ/

fuller's earth (uncountable)

1. A fine clay used in fulling cloth.
   • 1785 October 17, The Times, page 3 col. D:

     On Lord Sunderland's estate, in the county of Westmeath, there is a fine strata of fuller’s earth, a commodity of which our woollen manufacturers stand much in need: yet this bed lies unnoticed to all, except the peasantry on the soil.

   • 1892, Arthur Conan Doyle, The Adventure of the Engineer's Thumb‎:

     You are probably aware that fuller’s earth is a valuable product, and that it is only found in one or two places in England?

• walker's earth (rare)