A sling is a cupped piece of leather tied to cords or thongs, and used as a hand catapult for throwing stones. In Society heraldry, the one registration to date is of a hand sling (à la David and Goliath); the cup is to base and thongs to chief by default.
In period heraldry, there is also the “slingstaff”: essentially a hand sling fastened to a long pole, with a hook to hold the sling closed until released. This form is a period charge, found in the arms of Curdon or Cawarden c.1520 [DBA1 9; cf. Parker 542]. See also weapons.
Rikk Starhurler bears: Vert, in bend sinister a sinister hand couped inverted grasping a sling proper, therein a mullet of four points Or.