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.
A metal device with four projecting spikes so arranged that when three of the spikes are on the ground, the fourth points upward, used as a hazard to pneumatic tires or to the hooves of horses.
[Middle English calketrappe, from Norman French and from Old English calcatrippe, thistle, both from Medieval Latin calcatrippa, thistle : possibly from Latin calcāre, to tread on; see calque + trappa, trap (of Germanic origin).]
water chestnut n.
A floating aquatic plant (Trapa natans) native to Eurasia and Africa, bearing four-pronged nutlike fruit and grown as a pond or aquarium ornamental. Also called caltrop, water caltrop.
A tropical Asian aquatic sedge (Eleocharis dulcis) having an edible corm and cylindrical leaves.
The succulent corm of this plant, used in Asian cooking. Also called Chinese water chestnut.
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