acontium

from The Century Dictionary.

• noun In Greek antiquity: A dart or javelin, smaller and lighter than the long spear, and thrown by means of a thong or amentum. Hence—
• noun The game of hurling the javelin, one of the five exercises of the famous pentathlon (which see) at the Olympian, Isthmian, and other games.—
• noun plural in zoology, convoluted cords formed in the Actinia and furnished with thread-cells.