From The Collaborative International Dictionary of English v.0.48:
Bolas \Bo"las\, n. sing. & pl. [Sp.]
A kind of missile weapon consisting of one, two, or more
balls of stone, iron, or other material, attached to the ends
of a leather cord; -- used by the Gauchos of South America,
and others, for hurling at and entangling an animal.
[1913 Webster]