noun1. any tropical or subtropical plant of the zygophyllaceous genera Tribulus and Kallstroemia that have spiny burs or bracts
 2.  water caltrop
3.   another name for the star thistle
4.  military a four-spiked iron ball or four joined spikes laid upon the ground as a device to lame cavalry horses, puncture tyres, etc
   Word origin
Old English 
calcatrippe (the plant), from Medieval Latin 
calcatrippa, probably from Latin 
calx heel + 
trippa trap1