A genus of herbaceous plants (Tribulus) of the order Zygophylleæ, having a hard several- celled fruit, armed with stout spines, and resembling the military instrument of the same name. The species grow in warm countries, and are often very annoying to cattle.
- Any of various plants of the genera Tribulus and Kallstroemia, having spiny or tuberculate fruits.
- A Mediterranean species of star thistle (Centaurea calcitrapa) naturalized in North America.
- See water chestnut.
- A metal device with four projecting spikes so arranged that when three of the spikes are on the ground, the fourth points upward, used as a hazard to pneumatic tires or to the hooves of horses.