trĭbŭlus (trĭbŏl-), i, m., = τρίβολος, an instrument resting on three of its iron prongs, while a fourth projected upward, thrown on the ground to impede an enemy's cavalry, a caltrop.
I Lit.: tribulos abjecerunt, Veg. Mil. 3, 24.—
II Transf., from its resemblance in form.
A A kind of thorn or thistle , land-caltrops : Tribulus terrestris, Linn.; Verg. G. 1, 153; Ov. M. 13, 803; Plin. 21, 15, 54, § 91: spinae et tribuli, Vulg. Gen. 3, 18.—
B A kind of water-plant bearing a prickly nut of a triangular form, water - chestnut , water - caltrops : Trapa natans, Linn.; Plin. 21, 16, 58, § 98.