Source : Webster's Revised Unabridged Dictionary (1913)

Parthian \Par"thi*an\, a.
   Of or pertaining to ancient Parthia, in Asia. -- n. A native
   Parthia.

   {Parthian arrow}, an arrow discharged at an enemy when
      retreating from him, as was the custom of the ancient
      Parthians; hence, a parting shot.