From WikipediaWhere did the term called pistols come from?
A pistol is a handgun, more specifically one with the chamber integral to its gun barrel, though in common usage the two terms are often used interchangeably. The English word was introduced in ca. 1570, when early handguns were produced in Europe, and is derived from the Middle French pistolet (ca. 1550), meaning a small gun or knife. In colloquial usage, the word "pistol" is often used to describe any type of handgun, inclusive of revolvers (which have a single barrel and a separate cylinder housing multiple chambers) and the pocket-sized derringers (which are often multi-barrelled).
The most common type of pistol used in the contemporary era is the semi-automatic pistol, while the older single-shot and manual repeating pistols are now rarely seen and used primarily for nostalgic hunting and historical reenactment, and the fully automatic machine pistols are uncommon in civilian usage due to generally poor recoil-controllability and strict laws and regulations governing their manufacture and sale.
Technically speaking, the term "pistol" is a hypernym generally referring to a handgun and predates the existence of the type of guns to which it now applied as a specific term, that is: in colloquial usage it is used as a hyponym to specifically describe pistols with a single integral chamber within its barrel. The American Webster's Dictionary defines it as "a handgun whose chamber is integral with the barrel". This makes it distinct from the other types of handgun, such as the revolver, which has multiple chambers within a rotating cylinder that are separately aligned with a single barrel; and the derringer, which is a short pocket gun often with multiple single-shot barrels and no reciprocating action. The Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) legally defines the term "pistol" as "a weapon originally designed, made, and intended to fire a projectile (bullet) from one or more barrels when held in one hand, and having: a chamber(s) as an integral part(s) of, or permanently aligned with, the bore(s); and a short stock designed to be gripped by one hand at an angle to and extending below the line of the bore(s)", which includes derringers but excludes revolvers.
In contrast with modern colloquial usage, the term is technically synonymous with any handgun type, including all revolvers and derringers. UK/Commonwealth usage, for instance, does not usually make distinction, particularly when the terms are used by the military. For example, the official designation of the Webley Mk VI revolver was "Pistol, Revolver, Webley, No. 1 Mk VI". In contrast to the Merriam-Webster definition, the Oxford English Dictionary (a descriptive dictionary) describes "pistol" as "a small firearm designed to be held in one hand", which is similar to the Webster definition for "handgun"; and "revolver" as "a pistol with revolving chambers enabling several shots to be fired without reloading", giving its original form as "revolving pistol"