The term arming-sword refers not so much to a sword design as the situation under which the sword was used. Several different types of long-sword and bastard-sword carried by European knights could be called arming-swords and a better term may be "knight's-sword". These were worn by a knight even when not in armor, and he would be considered 'undressed' for public if he were without his arming sword. In the battle field, the arming sword was his secondary sword, usually behind a primary bastard-sword

Although a variety of designs fall under the heading of 'arming sword', they are most commonly thought of as single handed double edged long-swords more for cutting and hacking than for thrusting. Some were of slightly broader blade and less pointed tip than contemporary long-swords. These inevitably fell under the catch-all heading of 'broad sword' erroneously appointed by later scholars.