What is "kestros"

A kestros or kestrophedrone, also known as a cestrus or cestrosphendone, is a specially designed sling that is used to throw a heavy kind of dart.

The dart would typically consist of a heavy metal point approximately nine inches (22.9 cm) long, attached to a shaft of wood, typically twelve inches (30.5 cm) long, and fletched with feathers or the like to provide stability of flight.