The Collaborative International Dictionary of English v.0.48:

Brown bill \Brown" bill`\ [Brown + bill cutting tool.]
   A bill or halberd of the 16th and 17th centuries. See 4th
   Bill.
   [1913 Webster]

         Many time, but for a sallet, my brainpan had been cleft
         with a brown bill.                       --Shak.
   [1913 Webster]

   Note: The black, or as it is sometimes called, the brown
         bill, was a kind of halberd, the cutting part hooked
         like a woodman's bill, from the back of which projected
         a spike, and another from the head. --Grose.
         [1913 Webster]