caltrop /ˈkaltɹəp/ noun3 •A metal object, usually small, with spikes arranged so that, when thrown onto the ground, one always faces up as a threat to pedestrians, horses, and vehicles (also used as a heraldic charge).[…] her father, the emperor Alexius, who reigned AD 1081-1118, ordered caltrops to be cast in front of his archers […] — 1858 •The starthistle, Centaurea calcitrapa, a plant with sharp thorns. •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. formscaltrops
