Lewis & Short

jăcŭlus, a, um, adj. [jacio], that is thrown (mostly subst.). So, rete jaculum and simply jaculum, a casting-net, fishingnet, Plaut. Truc. 1, 1, 14; id. As. 1, 1, 86; cf.: hi jaculo pisces, illi capiuntur ab hamis, Ov. A. A. 1, 763.
Also of the net of the gladiator retiarius, Isid. Orig. 18, 54.
Hence, subst.: jăcùlus, i, m.

  1. A. (Sc. serpens.) A serpent that darts from a tree on its prey: jaculi volucres, Luc. 9, 720; 9, 822; Plin. 8, 23, 35, § 85.
  2. B. Jaculus (sc. funis or laqueus), a sling or noose which is thrown over the horns of oxen, a lasso, Col. 6, 2, 4 (al. laquei).