Definition of "caltrop" []

• Any of various plants of the genera Tribulus and Kallstroemia, having spiny or tuberculate fruits. (noun)
• A Mediterranean species of star thistle (Centaurea calcitrapa) naturalized in North America. (noun)
• See water chestnut. (noun)
• 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. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Speaking of mood, the play's climactic slaughterfest (in which solids, gases, liquids and something called a caltrop all prove excellent murder weapons) inevitably seems funny today."
• "In some few caterpillars the poison spines take the form of balls armed with short prickles and one large spike; hence they are known as caltrop spines (fig. 2, C), from their likeness to the cruel weapons, known as caltrops, which used to be scattered over the ground in time of war to repel the attacks of cavalry; the spikes forced their way into the horses 'feet when trampled on, and so disabled them."
• "Sooner or later, the worm forsakes this kind of caltrop which catches on to everything."