Caltrap

1. n. An instrument with four iron points, so disposed that, any three of them being on the ground, the other projects upward. They are scattered on the ground where an enemy’s cavalry are to pass, to impede their progress by endangering the horses’ feet.
2. n. A genus of herbaceous plants (Tribulus) of the order Zygophylleae, 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.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.