Pronunciation: (kal'trup), [key]
1. any of several plants having spiny heads or fruit, as those of the genera Tribulus and Kallstroemia, or the star thistle, Centaurea calcitrapa.
2. an 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. Also,cal•thropPronunciation: (kal'thrup), [key] cal'trap.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.