The Collaborative International Dictionary of English v.0.48:

Bull \Bull\, n. [OE. bulle, fr. L. bulla bubble, stud, knob,
   LL., a seal or stamp: cf. F. bulle. Cf. Bull a writing,
   Bowl a ball, Boil, v. i.]
   1. A seal. See Bulla.
      [1913 Webster]

   2. A letter, edict, or respect, of the pope, written in
      Gothic characters on rough parchment, sealed with a bulla,
      and dated "a die Incarnationis," i. e., "from the day of
      the Incarnation." See Apostolical brief, under Brief.
      [1913 Webster]

            A fresh bull of Leo's had declared how inflexible
            the court of Rome was in the point of abuses.
                                                  --Atterbury.
      [1913 Webster]

   3. A grotesque blunder in language; an apparent congruity,
      but real incongruity, of ideas, contained in a form of
      expression; so called, perhaps, from the apparent
      incongruity between the dictatorial nature of the pope's
      bulls and his professions of humility.
      [1913 Webster]

            And whereas the papist boasts himself to be a Roman
            Catholic, it is a mere contradiction, one of the
            pope's bulls, as if he should say universal
            particular; a Catholic schimatic.     --Milton.
      [1913 Webster]

   The Golden Bull, an edict or imperial constitution made by
      the emperor Charles IV. (1356), containing what became the
      fundamental law of the German empire; -- so called from
      its golden seal.
      [1913 Webster]

   Syn: See Blunder.
        [1913 Webster]