CALTROP
- any of several plants having spiny heads or fruit, as those of the genera Tribulus and Kallstroemia, or the star thistle, Centaurea calcitrapa
- iron ball with four projecting spikes so disposed that when the ball is on the ground one of them always points upward: used to obstruct the passage of cavalry, armored vehicles, etc.
- a spiny plant, also CALTHROP, CALTRAP [n -S]
- a spiny plant [n CALTROPS]