1) Area denial weapon 2) Medieval weapon 3) Naturalized in America 4) Serious pasture weed 5) Subshrub 6) Suffrutex 7) Tire-puncturing strip 8) Tribulus terestris 1) Ling 
A caltrop (also known as caltrap, galtrop, cheval trap, galthrap{cn|date=July 2014}, galtrap, calthrop, crow`s foot) is an antipersonnel weapon made up of two or more sharp nails or spines arranged in such a manner that one of them always points upward from a stable base (for example, a tetrahedron). Caltrops were part of defenses that served to ....
• (n.) Alt. of Caltrap
A four pointed metal spike that was thrown on the ground, always with one spike upright. Used against cavalry horses.
Caltrops (also known as caltrap, galtrap or chevaltrap) were small iron balls with projecting spikes used in medieval warfare. The ground over which an enemy was expected to advance was thickly strewn with caltrops with the effect that advancing horses or bare-footed infantry were quickly disabled by the spikes penetrating their feet. Caltrops were...
[n] - tropical annual procumbent poisonous subshrub having fruit that splits into five spiny nutlets
devil`s weed noun tropical annual procumbent poisonous subshrub having fruit that splits into five spiny nutlets; serious pasture weed