Emily Dickinson Lexicon

BAC, or BACK, n. [D. bak, a bowl or cistern.]

1. In navigation, a ferry-boat or praam.
2. In brewing, a large flat tub, or vessel, in which wort is cooled before boiling; hence called a cooler.
3. In distilleries, a vessel into which the liquor to be fermented is pumped from the cooler, in order to be worked with the yeast.