A backsword is a sword with a blade on one edge, or an "edge-and-a-quarter."[1] The back of the sword is often the thickest part of the blade and acts to support and strengthen it.
The term refers more specifically to early modern European weapons, usually straight, and typically with complex protective hilts as used in George Silver's manuscripts.[2] It can also refer to the singlestick, which is used to train for fighting with the backsword, or to the sport or art of fighting in this fashion.[3]
Backswords were often the secondary weapons of European-style cavalrymen beginning in the late 16th and early 17th centuries.[1] Though some claim the weapon's name was derived from the practice of slinging the weapon in a scabbard behind the trooper's back while riding in order to prevent it from clanging against his or the horse’s side as they galloped, this is incorrect. It is simply a reference to the flat "back" or "spine" of the unsharpened edge. Cavalry armed with a sword carried them either slung from the waist or attached to the saddle, as common sense and a little practice demonstrates that wearing the blade down the back would make the weapon very difficult to draw, and could at worst lead to a very nasty cut or the loss of an ear.
Backswords were also carried by some infantrymen, including irregulars like the Highland Scots, who likewise wore them slung from the hip, most often in an across-the-shoulder baldric or sword belt. In Scottish Gaelic, they are called "claidheamh cuil" (back sword), one of several terms for distinct types of weapons they used. (For more information on this topic, see Claymore.)