A Caltrop

1. (weaponry) 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. (heraldry) The same object represented as a heraldic charge.
3. (colloquial) 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.

(weaponry): caltrap, galtrop, cheval trap, galthrap, galtrap, calthrop, crow’s foot

(starthistle): knapweed

(Tribulus terrestris): puncturevine, cat's head, yellow vine, goathead, burra, gokharu, bindii.