Etymology
Borrowed from Ancient Greek ξυστόν (xustón, “spear, javelin”), of unknown origin. Potentially from Proto-Indo-European *ǵʰasto- or *ǵʰasdʰo- (“branch ~ spear, sharp spine”) (whence also gad, goad, and yard), but this is likely a substrate word in view of the various irregularities.
Definitions & examples from Wiktionary (CC BY-SA 3.0).