caltrop

noun

• 1a spiked metal device thrown on the ground to impede wheeled vehicles or (formerly) cavalry horses: militant demonstrators threw a box of caltrops across the highway

• 2a creeping plant with woody carpels that typically have hard spines and resemble military caltrops.

  • Genus Tribulus, family Zygophyllaceae

• 3 (also water caltrop)another term for water chestnut (sense 3).