Kindjal

A Kindjal is a slightly curved double-edged long knife or short sword, with a blade approximately 20cm long. Many family members of Great Houses were taught how to wield this weapon during the days of the Faufreluches.

Duke Leto Atreides carried such a weapon on his person.

Stats
Blade length: ca. 20 cm

Mass: 0.25 - 0.3 kilograms

Behind the Scenes
The kindjal is modeled on the Caucasian khanjali (kinzhal in Russian), a long-double edged knife part of traditional dress and often used in duels. Traditional kindjals often have a blade length of 42-55 cm, almost twice as long as the Kindjals of the Dune books.

In Expanded Dune, the Kindjal is a type of fighter starcraft.

In Emperor: Battle for Dune game House Attreides is known to deploy kindjal infantry. These high tier infantry are armed with a pistol for mobile fighting and a heavy antimaterial rifle when in deployed formation.

It is unclear what Herbert meant by the kindjal being "double-bladed". If taken literally it suggests that the knife has two blades, one at each end of the hilt. However, Herbert's reference to "20 centimeters of slightly curved blade" seems to indicate that "double-bladed" means double-edged, or sharp on both sides. In addition, kindjals are never refered to elsewhere as having two blades, making the second explanation more likely.