caltrop

noun

1. A small, metal object with spikes arranged so that, when thrown onto the ground, one always faces up as a threat to pedestrians, horses, and vehicles.
2. The same object represented as a heraldic charge.
3. The starthistle, Centaurea calcitrapa, a plant with sharp thorns.
4. Any of a number of flowering plants in the family Zygophyllaceae, including several members of the genus Kallstroemia and the species Tribulus terrestris, native to warm temperate and tropical regions.