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.

Source : WordNet®

Parthian
     adj 1: pertaining to Parthia or its people or language or culture;
            "Parthian archeology"
     2: delivered at the moment of parting as if in flight or
        retreat; "paused to deliver a parting shot at the door";
        "a Parthian volley of expletives from Uncle Billy"- Bret
        Harte [syn: {parting}]
     n : a native or inhabitant of Parthia