3. a sauce, or similar preparation, composed of various ingredients mixed in a sloppy mass
to sponge (slang)
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from slap vb. (to lap or gobble up) + sauce n.
From: A Collection of Scarce and Valuable Tracts,
on the Most Interesting and Interesting Subjects,
Revised, Augmented, and Arranged by Walter Scott, 1810
Tracts during the Reign of King James, Miscellaneous Tracts