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|Literal meaning||butterfly double sword|
The butterfly sword is a short dao,or single-edged sword,originally from southern China,though it has also seen use in the north. It is thought that butterfly swords date from the early 19th century. Several English language accounts from the 1840s describe local militia in Guangdong being trained in the "double swords",short swords with a hook extending from the guard,and fitting into a single scabbard. 
The blade of a butterfly sword is roughly as long as a human forearm,which allows easy concealment inside loose sleeves or boots,[ citation needed ] and allows greater maneuverability when spinning and rotating during close-quarters fighting.  Butterfly swords are usually wielded in pairs. A pair of swords will often be carried side by side within the same scabbard,so as to give the appearance of a single weapon.
The butterfly sword has a small crossguard to protect the hands of the wielder,similar to that of a sai,which can also be used to block or hook an opponent's weapon. In some versions the crossguard is enlarged offering a second handhold,held in this position the swords can be manipulated in a manner akin to a pair of tonfa. They may also be used as brass knuckles when non-lethal application of the weapon is desired.
Traditionally,the blade of a butterfly sword is only sharpened along half of its edge –from the middle of the blade to the tip;this can be seen in all vintage specimens from the Qing dynasty.[ citation needed ] The blade from the midpoint down is left blunt so that it can be used to deliver non-lethal strikes and to block without damaging the sharpened edge.[ citation needed ] Butterflies were generally commissioned for individual martial artists,not mass-produced,so every set of swords is different;[ citation needed ] however,an average blade today is about 11+1⁄2" long with a 6" handle.
Butterfly swords are usually called 'butterfly knives' in English. However, they should not be confused with the folding balisong, which is also commonly called a butterfly knife. The Chinese word dao is used to designate any blade whose primary function is to cut and slash regardless of length. In some branches of Kung Fu, such as Wing Chun, butterfly knives are known as Baat Jaam Do (named after the system's form, literally 'Eight Chopping/Slashing Knives' in Cantonese).
Butterfly swords are used in several Chinese martial arts, notably Wing Chun, Hung Ga, and Choy Li Fut. In Wing Chun, one notable aspect of butterfly sword combat is that its principles are the basis for all other weaponry. In theory, any object that can be held in the hands of a Wing Chun practitioner will follow the same basic principles of movement as the butterfly swords. This is because the use of butterfly swords is simply an extension of empty-handed combat. 
The design of the weapon, including the quillon (crossguard) shape, blade profile and blade length, are specific to each style of martial arts, the precise lineage, and individual.  For example, some martial arts lineages flip the butterfly swords between the forward and reverse grip like a Sai, and consequently need a quillon that will fit the hand during a reverse grip. Some lineages trap the opponent's staff or blade between the quillon and spine, and they need a longer quillon closer and more parallel to the spine than would fit a hand after flipping. Some schools like a hybrid quillon design that is adequate for both flipping and trapping, but optimal for neither.
Some butterfly swords had a long narrow blade that emphasized stabbing. While a deadly stabbing blade with a sharpened point—known as "Red Boat" knives—was used by Chinese revolutionaries in the Wing Chun lineage, modern Wing Chun practitioners tend to prefer a blade profile with a wider belly that emphasizes chopping and slashing. Wing Chun lore attributes this to the desire of Monks to maim rather than kill. These knives generally have a quarter circle style tip suitable only for chopping/slashing and not stabbing, or a shallower curve to a more pointed tip that will accommodate both. 
The appropriate length of the blade is a combination of the lineage and individual. For a Hung Gar stylist, the length should be a few inches past the elbow when the knife is held in a reverse grip. Wing Chun schools that use techniques which twirl the knives inside the arm need a reverse grip blade length based on the distance to the interior of the bicep. Other Wing Chun schools measure to the outside of the bicep.
A dagger is a fighting knife with a very sharp point and usually two sharp edges, typically designed or capable of being used as a thrusting or stabbing weapon. Daggers have been used throughout human history for close combat confrontations, and many cultures have used adorned daggers in ritual and ceremonial contexts. The distinctive shape and historic usage of the dagger have made it iconic and symbolic. A dagger in the modern sense is a weapon designed for close-proximity combat or self-defense; due to its use in historic weapon assemblages, it has associations with assassination and murders. Double-edged knives, however, play different sorts of roles in different social contexts.
A sword is an edged, bladed weapon intended for manual cutting or thrusting. Its blade, longer than a knife or dagger, is attached to a hilt and can be straight or curved. A thrusting sword tends to have a straighter blade with a pointed tip. A slashing sword is more likely to be curved and to have a sharpened cutting edge on one or both sides of the blade. Many swords are designed for both thrusting and slashing. The precise definition of a sword varies by historical epoch and geographic region.
The kukri or khukuri is a type of short sword with a distinct recurve in its blade originated in the Indian subcontinent. It serves multiple purposes as a melee weapon and also as a regular cutting tool throughout most of South Asia. The kukri, khukri, and kukkri spellings are of Indian English origin, with the original Nepalese English spelling being khukuri.
The jian is a double-edged straight sword used during the last 2,500 years in China. The first Chinese sources that mention the jian date to the 7th century BCE, during the Spring and Autumn period; one of the earliest specimens being the Sword of Goujian. Historical one-handed versions have blades varying from 45 to 80 centimeters in length. The weight of an average sword of 70-centimetre (28-inch) blade-length would be in a range of approximately 700 to 900 grams. There are also larger two-handed versions used for training by many styles of Chinese martial arts.
Dao are single-edged Chinese swords, primarily used for slashing and chopping. They can be straight or curved. The most common form is also known as the Chinese sabre, although those with wider blades are sometimes referred to as Chinese broadswords. In China, the dao is considered one of the four traditional weapons, along with the gun, qiang (spear), and the jian, called in this group "The General of Weapons".
The French estoc is a type of sword, also called a tuck in English, in use from the 14th to the 17th century. It is characterized by a cruciform hilt with a grip for two-handed use and a straight, edgeless, but sharply pointed blade of around 0.91 metres (36 in) to 1.32 metres (52 in) in length. It is noted for its ability to pierce mail armor.
A tantō is one of the traditionally made Japanese swords that were worn by the samurai class of feudal Japan. The tantō dates to the Heian period, when it was mainly used as a weapon but evolved in design over the years to become more ornate. Tantō were used in traditional martial arts. The term has seen a resurgence in the West since the 1980s as a point style of modern tactical knives, designed for piercing or stabbing.
These are terms used in the Chinese martial art, Wing Chun. They are originally colloquial Cantonese. Thus, their meanings might be difficult to trace. Some of those terms are used in Jeet Kune Do, sometimes with a different meaning.
The English language terminology used in the classification of swords is imprecise and has varied widely over time. There is no historical dictionary for the universal names, classification, or terminology of swords; a sword was simply a double-edged knife.
A ricasso is an unsharpened length of blade just above the guard or handle on a knife, dagger, sword, or bayonet. Blades designed this way appear at many periods in history in many parts of the world and date back to at least the Bronze Age—essentially, as long as humans have shaped cutting tools from metals.
A kalis is a type of double-edged Philippine sword, often with a "wavy" section. The kalis has a double-edged blade, which is commonly straight from the tip but wavy near the handle. Kalis with fully straight or fully wavy blades also exist. It is similar to the Javanese keris, but differs in that the kalis is a sword, not a dagger. It is much larger than the keris and has a straight or slightly curved hilt, making it primarily a heavy slashing weapon.
The Fairbairn–Sykes fighting knife is a double-edged fighting knife resembling a dagger or poignard with a foil grip. It was developed by William Ewart Fairbairn and Eric Anthony Sykes in Shanghai based on ideas that the two men had while serving on the Shanghai Municipal Police in China before World War II.
On a sword, the crossguard, or cross-guard, the individual bars on either side known as quillon, is a bar of metal at right angles to the blade, placed between the blade and the hilt.
The hook sword, twin hooks, fu tao, hu tou gou or shuang gou is a Chinese weapon traditionally associated with northern styles of Chinese martial arts and Wushu weapons routines, but now often practiced by southern styles as well.
Dha is the Burmese word for "knife" and "sword" similar term to daab or darb in Thai language for a single edge sword. The term dha is conventionally used to refer to a wide variety of knives and swords used by many people across Southeast Asia, especially present-day Myanmar (Burma), Thailand, Yunnan, Laos, Cambodia and Vietnam.
A knife fight is a violent physical confrontation between two or more combatants in which one or more participants is armed with a knife. A knife fight is defined by the presence of a knife as a weapon and the violent intent of the combatants to kill or incapacitate each other; the participants may be completely untrained, self-taught, or trained in one or more formal or informal systems of knife fighting. Knife fights may involve the use of any type of knife, though certain knives, termed fighting knives, are purposely designed for such confrontations – the dagger being just one example.
The Yanmaodao is a type of dao used as a standard military weapon during the Ming Dynasty and middle Qing Dynasty (1368–1800). The blade is straight until the curve begins around the center of percussion along the last 1/4 or so of the blade approaching the tip. The center of percussion is the point on the blade with the least vibration on hard contact, the spot on the blade that transmits the most power to the target in a hard chop. This allows for thrusting attacks and overall handling similar to that of the jian, while still preserving much of the dao's strengths in cutting and slashing. This type of sword seems to have lost its popularity with military and martial arts practitioners alike by the end of the 18th century.
The M3 trench knife or M3 fighting knife was an American military combat knife first issued in March 1943. The M3 was originally designated for issue to soldiers not otherwise equipped with a bayonet. However, it was particularly designed for use by forces in need of a close combat knife, such as Airborne Units and Army Rangers, so these units received priority for the M3 at the start of production. As more M3 knives became available in 1943 and 1944, the knife was issued to other soldiers such as Army Air Corps crewmen and soldiers not otherwise equipped with a bayonet, including soldiers issued the M1 carbine or a submachine gun such as the M3 "grease gun".
There are several Chinese martial arts known as Snake Boxing or Fanged Snake Style which imitate the movements of snakes. It is a style of Shaolin Boxing. Proponents claim that adopting the fluidity of snakes allows them to entwine with their opponents in defense and strike them from angles they would not expect in offense. Snake style is said to especially lend itself to applications with the Chinese straight sword. The snake is also one of the animals imitated in Yang family Taijiquan, Baguazhang and Xingyiquan. The sinuous, fluid motion of the snake lends itself to the practical theory that underlies the "soft" martial arts.
Ratings of the Royal Navy have used cutlasses, short, wide bladed swords, since the early 18th century. These were originally of non-uniform design but the 1804 Pattern, the first Navy-issue standard cutlass, was introduced at the start of the 19th century. This was a bluntish weapon that was perhaps intended for cutting away canvas and ropes rather than as a thrusting combat weapon. The 1845 Pattern cutlass introduced a bowl-style hand guard which provided greater protection, with a longer and more curved blade. Its sharper point made it more useful for thrusting attacks, which were now emphasised in the drill manual. The 1845 Pattern was modified several times including shortening and straightening the blades, which weakened them. The 1889 Pattern had a straight, spear-pointed blade with a hilt that curved outwards to catch and redirect an opponent's sword point. The 1900 Pattern, the last navy-issue cutlass, was similar to its predecessor with the introduction of a fuller and a hilt insert that cushioned the user's little finger. The cutlass was withdrawn from service in 1936 but remains in use for ceremonial purposes. It is thought that it was last used in combat in 1900 during the Boxer Rebellion.