Definition of: caltrop

(kal′trəp) noun
1. Mil. A small iron instrument shaped like a ball from which four sharp–pointed curved spikes project and are so mounted that one is always upright: formerly used to impede cavalry or infantry.
2. One of various plants with spiny heads or fruit that entangle the feet, as the hairy caltrop (Kalestroemia hirsutissima), the puncturevine, the star thistle, and the water chestnut. Also cal′trap (-trəp). [OE coltetraeppe <L calx heel + LL trappa trap]