1. Thick leather boots that go to the knee, used my military forces in the 17th, 18th, and 19th centuries.
2. Someone (usually a leader of military or police forces) that will do whatever it takes to accomplish their goals, the walking embodiment of "the ends justify the means".
1. The captain wore a pair of Jackboots with spurs to make his horse run faster.
2. The general sure is a jackboot, I hear he had 2 men whipped for leaving their post 2 minuets early