An English form of savon, the French for soap.
“A deputation of washwomen petitioned the Convention for soap, and
their plaintive cry was heard round the Salle de Manége, `Du pain er
du savon!' ” -
(Castile). A hard white soap made of olive oil, sometimes mottled with ferruginous matter. There are also Marseilles soap, Spanish soap, Venetian soap, and marine soap (usually made of cocoanut oil and used with sea-water).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894