1. A four sided die (d4) popular in role-playing games like Dungeons & Dragons.
"Ouch, Tom. Put your caltrop back into your dice bag..."
A metal ball that has 4 spikes arranged like the corners of a tetrahedron. Used for slowing calvalry. (The spikes stab into the horses hooves) I almost looks like a playing jack.
Sam layed the caltrops accross the roads and all the horses who ran through the road couldn't run anymore.