Online Etymology Dictionary

pistachio (n.): 1590s, from Italian pistacchio, from Latin pistacium "pistachio nut," from Greek pistakion "pistachio nut," from pistake "pistachio tree," from Persian pistah "pistachio." Borrowed earlier (1530s) as pystace, from Old French form pistace (13c.), which also is from the Italian word.
piste (n.): also pist, 1727, from French piste, from Latin pista (via) "beaten (track)," from pistus, past participle of pinsere "to pound, stamp" (see pestle).
pistil (n.): "female organ of a flower," 1718, from French pistil, from Modern Latin pistillum "a pistil," so called from resemblance to a pestle, from Latin pistillum "pestle" (see pestle). Related: Pistillary; pistillaceous; pistillate; pistilline.
pistle (n.): "letter," Old English pistol, a shortening of epistol, from Latin epistola (see epistle).
pistol (n.): "small hand-held firearm," 1570s, from Middle French pistole "short firearm" (1566), of uncertain origin, sometimes said to be from German Pistole, from Czech pis'tala "firearm," literally "tube, pipe," from pisteti "to whistle," of imitative origin, related to Russian pischal "shepherd's pipe."

But earlier English form pistolet (1550) is said to be from Middle French pistolet "a small firearm," also "a small dagger," which may be the literal sense; though some connect this word with Italian pistolese, in reference to Pistoia, town in Tuscany noted for gunsmithing. Pistol-whip (v.) is first recorded 1942.
pistole (n.): former Spanish coin (not called that in Spanish), 1590s, from French pistole, from Italian piastola, diminutive of piastra "plate or leaf of metal" (see piaster). Compare earlier pistolet (1550s) "foreign coin," which OED says is from French pistolet "short firearm" (see pistol) and so called for being smaller and thinner than other coins.
pistolero (n.): 1937, from Spanish; see pistolier.
pistolier (n.): also pistoleer, 1570s from obsolete French pistolier, from pistole (see pistol).
piston (n.): 1704, from French piston, from Middle French piston "large pestle," from Old Italian pistone "a piston," variant of pestone "a pestle," from pestare "to pound," from Late Latin pistare, frequentative of Latin pinsere (past participle pistus) "to pound" (see pestle). As a verb from 1930.
pit (n.1): "hole, cavity," Old English pytt "water hole, well; pit, grave," from Proto-Germanic *puttjaz "pool, puddle" (source also of Old Frisian pet, Old Saxon putti, Old Norse pyttr, Middle Dutch putte, Dutch put, Old High German pfuzza, German Pfütze "pool, puddle"), early borrowing from Latin puteus "well, pit, shaft." Meaning "abode of evil spirits, hell" is attested from early 13c. Pit of the stomach (1650s) is from the slight depression there between the ribs.
pit (n.2): "hard seed," 1841, from Dutch pit "kernel, seed, marrow," from Middle Dutch pitte, ultimately from Proto-Germanic *pithan-, source of pith (q.v.).
pit (v.): mid-15c., "to put into a pit," from pit (n.1); especially for purposes of fighting (of cocks, dogs, pugilists) from 1760. Figurative sense of "to set in rivalry" is from 1754. Meaning "to make pits in" is from late 15c. Related: Pitted; pitting. Compare Pit-bull as a dog breed attested from 1922, short for pit-bull terrier (by 1912). This also is the notion behind the meaning "the part of a theater on the floor of the house" (1640s).
pit-a-pat (adv.): also pitter-pat, 1520s; imitative. As a noun from 1580s.
pita (n.): "thick, flat bread," 1951, from Modern Hebrew pita or Modern Greek petta "bread," perhaps from Greek peptos "cooked," or somehow connected to pizza (q.v.).
pitch (n.2): "resinous substance, wood tar," late 12c., pich, from Old English pic "pitch," from a Germanic borrowing (Old Saxon and Old Frisian pik, Middle Dutch pik, Dutch pek, Old High German pek, German Pech, Old Norse bik) of Latin pix (genitive picis) "pitch," which according to Watkins is from a PIE root *pik- "pitch" (source also of Greek pissa, Lithuanian pikis, Old Church Slavonic piklu "pitch"), but according to Pokorny this is from the same PIE root as pine (n.). The English word was applied to pine resins from late 14c. Pitch-black is attested from 1590s; pitch-dark from 1680s.
pitch (v.1): c. 1200, "to thrust in, fasten, settle," probably from an unrecorded Old English *piccean, related to prick (v.). The original past tense was pight. Sense of "set upright," as in pitch a tent (late 13c.), is from notion of "driving in" the pegs. Meaning "incline forward and downward" is from 1510s. Meaning "throw (a ball)" evolved late 14c. from that of "hit the mark." Musical sense is from 1670s. Of ships, "to plunge" in the waves, 1620s. To pitch in "work vigorously" is from 1847, perhaps from farm labor. Related: Pitched; pitching.
pitch (n.1): 1520s, "something that is pitched," from pitch (v.1). Meaning "act of throwing" is attested from 1833. Meaning "act of plunging headfirst" is from 1762; sense of "slope, degree, inclination" is from 1540s; musical sense is from 1590s; but the connection of these is obscure. Sales pitch in the modern commercial advertising sense is from 1943, American English, perhaps from the baseball sense.
pitch (v.2): "to cover with pitch," Old English pician, from the source of pitch (n.2).
pitch-pipe (n.): 1711, from pitch (n.) in the musical sense + pipe (n.1).
pitchblende (n.): also pitch-blende, 1770, a loan-translation of German Pechblende; see pitch (n.2) + blende.
pitcher (n.1): "earthen jug," c. 1200, from Old French pichier (12c.), altered from bichier, from Medieval Latin bicarium, probably from Greek bikos "earthen vessel" (see beaker). Pitcher-plant is recorded from 1819; so called for its resemblance.
pitcher (n.2): "one who pitches," 1722, agent noun from pitch (v.1). Originally of one tossing hay into a wagon, etc.; baseball sense first recorded 1845.
pitchfork (n.): mid-14c., altered (by influence of pichen "to throw, thrust;" see pitch (v.1)) from Middle English pic-forken (c. 1200), from pik (see pike (n.4)) + fork (n.). The verb is attested from 1837.
pitchman (n.): 1926, American English, from pitch (n.1) in the sales sense + man (n.).
piteous (adj.): c. 1300, from Anglo-French pitous, Old French pitos "pious; merciful, compassionate, moved to pity; pitiful" (12c., Modern French piteux), from Medieval Latin pietosus "merciful, pitiful," in Vulgar Latin "dutiful," from Latin pietas "dutiful conduct, compassion" (see piety). Related: Piteously; piteousness.
pitfall (n.): c. 1300, "concealed hole," a type of animal trap, from pit (n.1) + fall (n.). Extended sense of "any hidden danger" is first recorded early 15c.
pith (n.): Old English piþa "pith of plants," also "essential part," from West Germanic *pithan- (source also of Middle Dutch pitte, Dutch pit, East Frisian pit), a Low German root of uncertain origin. Figurative sense was in Old English. Pith helmet (1889, earlier pith hat, 1884) so called because it is made from the dried pith of the Bengal spongewood.
pith (v.): "to kill by piercing the spinal cord," 1805, from pith (n.). Related: Pithed; pithing.
pithecanthropus (n.): genus of extinct primates, 1895, from Modern Latin, literally "monkey-man," from Greek pithekos "ape" + anthropos "man" (see anthropo-). Coined 1868 by Haeckel as a name for a hypothetical link between apes and men (attested in English in this sense from 1876); applied by Dr. Eugène Dubois (1858-1940), physician of the Dutch army in Java, to remains he found there in 1891.
pitheco-: before vowels pithec-, word-forming element meaning "pertaining to an ape or monkey," from Greek pithekos "ape."
pithy (adj.): early 14c., "strong, vigorous," from pith (n.) + -y (2). Meaning "full of substance or significance" is from 1520s; literal meaning "full of pith" not attested until 1560s. Related: Pithily; pithiness.
pitiable (adj.): mid-15c., "merciful, compassionate," from Old French piteable "compassionate, merciful, pious" (13c.; Modern French pitoyable), from piteer "to pity" (see pity). Meaning "deserving pity" is recorded from late 15c. Related: Pitiably.
pitiful (adj.): c. 1300, "merciful, compassionate" (implied in pitifully), from pity + -ful. Sense of "exciting or deserving pity" is from mid-15c.; that of "mean, wretched, contemptible" is 1580s. Related: Pitifulness.
pitiless (adj.): early 15c., from pity + -less. Related: Pitilessly; pitilessness.
piton (n.): 1898, from French piton "hook, peak of a mountain, piton, eyebolt," in Old French "nail, hook," from Vulgar Latin root *pitt- "point, peak" [Barnhart].
pits (n.): "the worst," by 1953, U.S. slang, said to be a shortened form of armpits.
pittance (n.): c. 1200, "pious donation to a religious house or order to provide extra food; the extra food provided," also "a small portion, scanty rations," from Old French pitance "pity, mercy, compassion; refreshment, nourishment; portion of food allowed a monk or poor person by a pious bequest," apparently literally "pity," from pitié (see pity). Meaning "small amount, portion" first recorded 1560s.
pituitary (adj.): 1610s, from Latin pituitarius "mucous," from pituita "clammy moisture, phlegm, mucus, slime," possibly from a suffixed form of PIE root *peie- "to be fat, swell" (see fat (adj.)). Taken as the name for the gland because it was believed that it channeled mucus to the nose. As a noun by 1899.
pity (n.): early 13c., from Old French pite, pitet "pity, mercy, compassion, care, tenderness; pitiful state, wretched condition" (11c., Modern French pitié), from Latin pietatem (nominative pietas) "piety, loyalty, duty" (see piety). Replaced Old English mildheortness, literally "mild-heartness," itself a loan-translation of Latin misericordia. English pity and piety were not fully distinguished until 17c. Transferred sense of "grounds or cause for pity" is from late 14c.
pity (v.): "to feel pity for," late 15c., from Old French pitier and from pity (n.). Related: Pitied; pitying.
Pius: masc. proper name, from Latin pius "dutiful, pious" (see pious).
pivot (n.): 1610s, from French pivot, from Old French pivot "hinge pin, pivot" (12c.), also "penis," of uncertain origin. Figurative sense of "central point" is recorded from 1813.
pivot (v.): by 1841, from French pivoter and from pivot (n). Related: Pivoted; pivoting.
pivotal (adj.): 1844, in figurative sense, from pivot (n.) + -al (1).
pix (n.): variant of pics, 1930 (see pic).
pixel (n.): 1969, coined to describe the photographic elements of a television image, from pix + first syllable of element.
pixelation (n.): also pixellation, graphics display effect, 1991, from pixel + -ation.
pixie (n.): c. 1630, of obscure origin, perhaps from or related to Swedish dialect pyske "small fairy," but West County origin suggests ultimate source in Cornwall and thus something Celtic. Earliest references were in pixy-path "bewilderment," literally "path on which one is led astray by pixies," and pixie-led "lost."
pixilated (adj.): "mildly insane, bewildered, tipsy," 1848, pix-e-lated, from pixie + -lated, as in elated, etc., perhaps influenced by or a variant of pixie-led. A New England dialect word popularized 1936 by its use in movie "Mr. Deeds Goes to Town."
pixilation (n.): "creation of the effect of animation in live actors," 1947, from pixilated. Also see pixelation.