The Collaborative International Dictionary of English v.0.48:

Bac \Bac\, n. [F. See Back a vat.]
   1. A broad, flat-bottomed ferryboat, usually worked by a
      rope.
      [1913 Webster]

   2. A vat or cistern. See 1st Back.
      [1913 Webster]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

BAC
       Basic Air Control (RFID)