A sword is a bladed weapon (edged weapon) used primarily for cutting or thrusting. The precise definition of the term varies with the historical epoch or the geographical region under consideration. A sword in the most narrow sense consists of a straight blade with two edges and a hilt. However, in nearly every case, the term may also be used to refer to weapons with a single edge (backsword).
The word sword comes from the Old English sweord, cognate to swert, Old Norse sverð, from a Proto-Indo-European root *swer- "to wound, to cut". Non-European weapons called "sword" include single-edged weapons such as the Middle Eastern saif, the Chinese dao and the related Japanese katana. The Chinese jian is an example of a non-European double-edged sword, like the European models derived from the double-edged Iron Age sword.
Historically, the sword developed in the Bronze Age, evolving from the dagger; the earliest specimens date to ca. 1600 BC. The Iron Age sword remained fairly short and without a crossguard. The spatha as it developed in the Late Roman army became the predecessor of the European sword of the Middle Ages, at first adopted as the Migration period sword, and only in the High Middle Ages developed into the classical arming sword with crossguard.