After my last heated debate concerning linguistics, I was hesitant to get involved in this discussion. However, I am more than adequately armed, so:
Pistol:
pistol - "small hand-held firearm," c.1570, from M.Fr. pistole "short firearm" (1566), of uncertain origin, sometimes said to be from Ger. Pistole, from Czech pis'tala "firearm," lit. "tube, pipe," from pisteti "to whistle," of imitative origin, related to Rus. pischal "shepherd's pipe." But earlier form pistolet (1550) is from M.Fr. pistolet "a small firearm," also "a small dagger," which may be the literal sense; though some connect this word with It. pistolese, in reference to Pistoia, town in Tuscany noted for gunsmithing. (Douglas Harper, consummate Etymologist)
"French pistole, from German, from Middle High German pischulle, from Czech pít'ala, pipe, whistle, firearm, from pitti, to whistle, of imitative origin." (Dictionary.com)
"A pistol is a usually small, hand held, projectile weapon, meant for personal use (used by one person) in short-range action. In the 15th Century, the term was used for small knives and daggers which could be concealed in a person's clothing. This may derive from the city of Pistoia, Italy, where daggers were manufactured. By the 18th century the term came to be used exclusively to refer to small firearms, or additionally, and more recently, similar devices designed for the aimed discharge of projectiles by the force of gas pressure stored by other than chemical means." (wikipedia)
"PISTOL
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) a chamber(s) as an integral part(s) of, or permanently aligned with, the bore(s); and (b) a short stock designed to be gripped by one hand and at an angle to and extending below the line of the bore(s)." (BATFE GLossary)
"REVOLVER
A projectile weapon of the
pistol type, having a breechloading chambered cylinder so arranged that the cocking of the hammer or movement of the trigger rotates it and brings the next cartridge in line with the barrel for firing." (BATFE Glossary)
And finally,
"Synonymous with "handgun." A gun that is generally held in one hand. It may be of the single-shot, multi-barrel, repeating or semi-automatic variety and
includes revolvers." (NRA Glossary)
By logical deduction, therefore, All Revolvers are Pistols, but not all Pistols are Revolvers