Definition of "caltrop"

caltrop

/ˈkæltɹəp/

noun
plural caltrops
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 (also used as a heraldic charge).
  Quotations
  […] her father, the emperor Alexius, who reigned AD 1081-1118, ordered caltrops to be cast in front of his archers […]
  1858, The journal of the British Archaeological Association
  By Sung times, several different types of caltrops had been developed. As in earlier times, both caltrops could be made from both wood and iron...
  1954, Joseph Needham, Ling Wang, Science and civilisation in China
  Caltrops, tetrahedrons, and similar devices are designed to puncture vehicle tires or limit foot traffic. The standard design has four points.
  2000, Alan Vick, Aerospace operations in urban environments: exploring new concepts
2. (colloquial) The starthistle, Centaurea calcitrapa, a plant with sharp thorns.
3. 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.