FULLER’S SOAP. An alkali prepared from the ashes of certain plants and used for cleansing and fulling new cloth. The word is used figuratively in
FULLER’s SOAP, Heb. phrase, וּכְבֹרִ֖ית מְכַבְּסִֽים, consisting of a term בֹּרִית, H1383, “alkaline salt,” “natural lye” extracted from the Asiatic soap plants such as Mesembrianthemum cristallinum; Salicornia solacea; Salsala kali and the like (cf. I. Löw, Die Flora der Juden [1924-1934]) which are reduced by burning to produce a pasty mass used as a bleach, esp. in the presence of olive oil. The other term is the common Sem. term כָּבַס, H3891, “to tread,” “knead” and thus to wash in the Near Eastern fashion.