The Collaborative International Dictionary of English v.0.48:

Banc \Banc\, Bancus \Ban"cus\, Bank \Bank\, n. [OF. banc, LL.
   bancus. See Bank, n.]
   A bench; a high seat, or seat of distinction or judgment; a
   tribunal or court.
   [1913 Webster]

   In banc, In banco (the ablative of bancus), In bank, in
      full court, or with full judicial authority; as, sittings
      in banc (distinguished from sittings at nisi prius).
      [1913 Webster]