The Collaborative International Dictionary of English v.0.48:

Horning \Horn"ing\, n.
   Appearance of the moon when increasing, or in the form of a
   crescent. --J. Gregory.
   [1913 Webster]

   Letters of horning (Scots Law), the process or authority by
      which a person, directed by the decree of a court of
      justice to pay or perform anything, is ordered to comply
      therewith. --Mozley & W.
      [1913 Webster]