The Collaborative International Dictionary of English v.0.48:

omnibus \om"ni*bus\, a.
   Pertaining to or dealing with a variety of topics at one
   time; as, omnibus legislation; an omnibus budget bill.
   [PJC]

   Omnibus bill, a legislative bill which provides for a
      number of miscellaneous enactments or appropriations.
      [Parliamentary Cant, U.S.]

   Omnibus box, a large box in a theater, on a level with the
      stage and having communication with it. [Eng.]
      --Thackeray.
      [1913 Webster]