Emily Dickinson Lexicon

CAL'TROP, n. [Sax. coltræppe, a species of Thistle, rendered by Lye, Rhamnus, and Carduus stellatus, The French has chaussetrape. The Italian calcatreppolo, is from calcare, to tread, and tribolo, a thistle; L. tribulus.]

1. A kind of Thistle, the Latin Tribulus, with a roundish prickly pericarp; on one side, gibbous, often armed with three or four daggers; on the other side, angular, converging with transverse cells. It grows in France, Italy, and Spain, among corn, and is very troublesome, as the prickles run into the feet of cattle. – Fam. of Plants. Miller.
2. In military affairs, an instrument with four iron points disposed in a triangular form, so that three of them being on the ground, the other points upward. These are scattered on the ground where an enemy's cavalry are to pass, to impede their progress by endangering the horses' feet. – Encyc. Dr. Addison.