means “salted food,” for giving a relish to meat, as pickled roots, herbs, and so on. (Latin, salsus.)
“After him another came unto her, and served her with the same sauce; then a third ...” —The Man in the Moon, etc. (1609).
(To). To intermix.
“Then she fell to sauce her desires with threatenings.” —Sidney.
“Folly sauced with discretion.” —
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894