1. a device with four sharp points arranged so that one always points upward, historically used to injure the feet of enemies or puncture tires
Usage: also spelled caltrop or caltrops (plural); historical/military context
2. any of various plants with spiny seed pods or fruits, especially of the genus Tribulus
Usage: botanical term

Examples

• Medieval soldiers scattered calthrops across the battlefield to slow down enemy cavalry.
• The road was littered with calthrops designed to puncture vehicle tires.
• Calthrop plants grow in arid regions and produce seeds with sharp spines.
• Police used calthrops to stop the fleeing suspect's car.
• The garden was invaded by calthrop weeds that were difficult to remove.