To take up the hatchet

from The Collaborative International Dictionary of English v.0.48
Hatchet \Hatch"et\ (-[e^]t), n. [F. hachette, dim. of hache ax.
   See 1st {Hatch}, {Hash}.]
   1. A small ax with a short handle, to be used with one hand.
      [1913 Webster]

   2. Specifically, a tomahawk.
      [1913 Webster]

            Buried was the bloody hatchet.        --Longfellow.
      [1913 Webster]

   {hatchet face}, a thin, sharp face, like the edge of a
      hatchet; hence:

   {hatchet-faced}, sharp-visaged. --Dryden.

   {To bury the hatchet}, to make peace or become reconciled.

   {To take up the hatchet}, to make or declare war. The last
      two phrases are derived from the practice of the American
      Indians.
    

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