Trigon, trigônis, Mar. A ball. A turtil. The sishe called a thornbacke.
Lewis and Short: Latin dictionary
trĭgōn, ōnis, m., = tri/gwn or tri/gwnon,a kind of ball for playing with, esp. in the baths, Mart. 4, 19, 5; 7, 72, 9; 12, 83, 3: fugio campum lusumque trigonem,