Back n.
 1. A large shallow vat; a cistern, tub, or trough, used by brewers, distillers, dyers, picklers, gluemakers, and others, for mixing or cooling wort, holding water, hot glue, etc.
 Hop back, Jack back, the cistern which receives the infusion of malt and hops from the copper.
 Wash back, a vat in which distillers ferment the wort to form wash.
 Water back, a cistern to hold a supply of water; esp. a small cistern at the back of a stove, or a group of pipes set in the fire box of a stove or furnace, through which water circulates and is heated.
 2. A ferryboat.  See Bac, 1.