[Fr.; see also BACK sb.2]
1. A flat-bottomed French ferry-boat; a ferry.
1672. Coles, Bac, a ferry.
1753. Chambers, Cycl. Supp., Bac, in navigation, is used for a praam, or ferry-boat.
1867. in Smyth, Sailors Word-bk. [Cf. St. Augustines Back at Bristol.]
2. In Brewing and Distilling: see BACK sb.2