caltrop

noun

1. an iron device with four spikes, placed on the ground so that one spike sticks up to hinder enemy cavalry
2. a similar device used to puncture pneumatic tires
3. any of a number of plants with spiny flowering parts or fruits; specif.,
   1. various plants (esp. Tribulus terrestris) of the caltrop family
   2. various plants of other families, as star thistle and water chestnut

Etymology: ME calketrappe < OE calcatrippe, star thistle & OFr chaucetrape, both < ML calcatrippa < L calcare, to tread upon (< calx, heel: see calcar) + Gmc *trippon, trip

adjective

designating a family (Zygophyllaceae) of dicotyledonous plants, shrubs, or trees (order Sapindales), including guaiacum, creosote bush, and bean caper