Parthian shot
noun
a sharp, telling remark, act, gesture, etc., made in departing.
Origin of Parthian shot
First recorded in 1900–05; so called from the ancient Parthian cavalry's habit of shooting arrows rearward at the enemy while in real or feigned flight
British Dictionary definitions for parthian shot
Word Origin for Parthian shot
alluding to the custom of Parthian archers who shot their arrows backwards while retreating