Boyd’s Bible Dictionary:
(sap, resin). The Hebrew word for soap implies any alkaline substance used for cleansing (Jer. 2:22; Mal. 3:2).
“Soap, Sope” From Concise Bible Dictionary:
Spoken of as used for cleansing the person, and as employed by the fuller (Jer. 2:22; Mal. 3:2). What its composition was is not now known.
“Sope” From Concise Bible Dictionary:
See SOAP.
Strong’s Dictionary of Hebrew Words:
Meaning:
feminine of 1253; vegetable alkali