Online Etymology Dictionary

plantigrade (adj.): 1831, from French plantigrade "walking on the sole of the foot" (1795), from Latin planta "sole of the foot" (see plant (n.)) + gradus "step" (see grade (n.)).
planting (n.): late Old English plantung "action of planting," also "a thing planted," verbal noun from plant (v.).
planxty (n.): in Irish music, "harp tune of a sportive and animated character" [OED], 1790, of unknown origin, evidently not a native Irish word; some suggest ultimate derivation from Latin plangere "to strike, beat" (see plague (n.)). See also [Katrin Thier, "Of Picts and Penguins -- Celtic Languages in the New Edition of the OED," in "The Celtic Languages in Contact," 2007.
plaque (n.): 1848, "ornamental plate or tablet," from French plaque "metal plate, coin" (15c.), perhaps through Flemish placke "small coin," from Middle Dutch placke "disk, patch, stain," related to German Placken "spot, patch" (cf. placard). Meaning "deposit on walls of arteries" is first attested 1891; that of "bacteria deposits on teeth" is 1898.
plaquemines: parish at the mouth of the Mississippi in Louisiana, U.S., from Louisiana French, literally "persimmon" (18c.), probably from Miami/Illinois (Algonquian) piakimina.
plash (v.1): "to splash," 1580s, from plash (n.) and also imitative (cf. Dutch plassen, German platschen). Related: Plashed; plashing.
plash (n.): "small puddle, shallow pool, wet ground," Old English plæsc "pool of water, puddle," probably imitative (cf. Dutch plass "pool"). Meaning "noise made by splashing" is first recorded 1510s.
plash (v.2): "to interlace," late 15c., from Old French plaissier, from Latin plectere "to plait" (see complex (adj.)). Related: Plashed; plashing.
plasm (n.): 1610s, "mold or matrix, cast;" see plasma. Meaning "living matter of a cell" is from 1864.
plasma (n.): 1712, "form, shape" (earlier plasm), from Late Latin plasma, from Greek plasma "something molded or created," hence "image, figure; counterfeit, forgery; formed style, affectation," from plassein "to mold," originally "to spread thin," from PIE *plath-yein, from root *pele- (2) "flat, to spread" (see plane (n.1)). Sense of "liquid part of blood" is from 1845; that of "ionized gas" is 1928.
plasmid (n.): 1952, from plasma + -id.
plasmodium (n.): 1871, Modern Latin, coined 1863 in Germany from plasma + -odium, from Greek -odes "like" (see -oid).
plasmolysis (n.): 1883, from French plasmolysis (1877), from plasmo- (see plasma) + Greek lysis "a loosening" (see -lysis). Related: Plasmolytic; plasmolyze.
plaster (n.): late Old English plaster "medicinal application," from Vulgar Latin plastrum, shortened from Latin emplastrum "a plaster" (in the medical as well as the building sense), from Greek emplastron "salve, plaster" (used by Galen instead of more usual emplaston), noun use of neuter of emplastos "daubed on," from en- "on" + plastos "molded," from plassein "to mold" (see plasma). The building construction material is first recorded in English c.1300, via Old French plastre, from the same source, and in early use the English word often had the French spelling.
plaster (v.): "to coat with plaster," early 14c., from plaster (n.) and partly Old French plastrier "to cover with plaster" (Modern French plâtrer), from plastre (see plaster (n.). Related: Plastered; plastering. Figurative use from c.1600. Meaning "to bomb (a target) heavily" is first recorded 1915. Sports sense of "to defeat decisively" is from 1919.
plaster of Paris (n.): mid-15c.; originally it was made from the extensive gypsum deposits of Montmartre in Paris.
plastered (adj.): "coated with plaster," late 14c., past participle adjective from plaster (v.). Slang meaning "very drunk" attested by 1912, perhaps from plaster in medical sense of "to apply a remedy to; to soothe" (see plaster (n.)).
plastic (n.): 1905, "solid substance that can be molded," originally of dental molds, from plastic (adj.). Main current meaning, "synthetic product made from oil derivatives," first recorded 1909, coined by Leo Baekeland (see bakelite).
plastic (adj.): 1630s, "capable of shaping or molding," from Latin plasticus, from Greek plastikos "able to be molded, pertaining to molding, fit for molding," also in reference to the arts, from plastos "molded, formed," verbal adjective from plassein "to mold" (see plasma). Surgical sense of "remedying a deficiency of structure" is first recorded 1839 (in plastic surgery). Meaning "made of plastic" is from 1909. Picked up in counterculture slang with meaning "false, superficial" (1963). Plastic explosive (n.) attested from 1894.
Plasticine: modeling clay substitute, 1897, from plastic (adj.) + -ine (2).
plasticity: 1782, from plastic + -ity.
plastid (n.): 1876, from German plastid, coined by Haeckel from Greek plastos "molded, formed" (see plaster) + -id.
plastron (n.): c.1500, from Middle French plastron "breastplate," from Italian piastrone, augmentative of piastra "breastplate, thin metal plate" (see piaster). As an animal part, from 1813; as an article of dress, 1876.
plat (n.): "piece of ground," 1510s, from plot (q.v.), assimilated to Middle English adjective plat "flat," which is from Old French plat "flat, stretched out" (see plateau (n.)). See OED for full explanation.
plat (v.): "to interweave," late 14c., variant of plait (v.). Related: Platted; platting.
plate (n.): mid-13c., "flat sheet of gold or silver," also "flat, round coin," from Old French plate "thin piece of metal" (late 12c.), from Medieval Latin plata "plate, piece of metal," perhaps via Vulgar Latin *plattus, formed on model of Greek platys "flat, broad" (see plaice (n.)). The cognate in Spanish (plata) and Portuguese (prata) has become the usual word for "silver," superseding argento via shortening of *plata d'argento "plate of silver, coin." Meaning "table utensils" (originally of silver or gold only) is from Middle English. Meaning "shallow dish for food," now usually of china or earthenware, originally of metal or wood, is from mid-15c. Baseball sense is from 1857. Geological sense is first attested 1904; plate tectonics first recorded 1969. Plate-glass first recorded 1727.
plate (v.): late 14c., from plate (n.). Related: Plated; plating.
plateau (v.): 1952, from plateau (n.). Related: Plateaued; plateauing.
plateau (n.): 1796, "elevated tract of relatively level land," from French plateau "table-land," from Old French platel (12c.) "flat piece of metal, wood, etc.," diminutive of plat "flat surface or thing," noun use of adjective plat "flat, stretched out" (12c.), perhaps from Vulgar Latin *plattus, from Greek platys "flat, wide, broad" (see plaice). Meaning "stage at which no progress is apparent" is attested from 1897, originally in psychology of learning. In reference to sexual stimulation from 1960.
platelet (n.): 1895, formed in English from plate + diminutive suffix -let.
platen (n.): 1540s, from Middle French plateine, from Old French platine "flat piece, metal plate" (13c.), perhaps altered (by influence of plat "flat") from patene, from Latin patena "pan."
platform (n.): 1540s, "plan of action, scheme, design," from Middle French plateforme, platte fourme, literally "flat form," from Old French plat "flat" (see plateau (n.)) + forme "form" (see form (n.)). The literal sense of "raised, level surface" in English is first recorded 1550s. Political meaning, "statement of party policies," is from 1803, probably originally an image of a literal platform on which politicians gather, stand, and make their appeals, perhaps influenced by earlier sense of "set of rules governing church doctrine" (first attested 1570s). Railroad station sense is from 1838.
platinum (n.): metallic element, 1812, Modern Latin, from Spanish platina "platinum," diminutive of plata "silver," from Old French plate or Old Provençal plata "sheet of metal" (see plate (n.)). The metal looks like silver, and the Spaniards at first thought it an inferior sort of silver, hence the name platina. It was first obtained from Spanish colonies in Mexico and Colombia, brought to Europe in 1735, and identified as an element 1741. Taken into English as platina (c.1750), it took its modern form (with element ending -ium) in 1812, at the time the names of elements were being regularized. As a shade of blond hair, attested from 1931. As a designation for a recording that has sold at least one million copies, it is attested from 1971.
platitude (n.): 1812, "dullness," from French platitude "flatness, vapidness" (late 17c.), from Old French plat "flat" (see plateau (n.)); formed on analogy of latitude, etc. Meaning "a flat, dull, or commonplace remark" is recorded from 1815. Related: Platitudinous. Hence platitudinarian (n.), 1855; platitudinize (1867).
Platonic (adj.): 1530s, "of or pertaining to Greek philosopher Plato" (429 B.C.E.-c.347 B.C.E.), from Latin Platonicus, from Greek Platonikos. The name is Greek Platon, properly "broad-shouldered" (from platys "broad;" see plaice (n.)). His original name was Aristocles. The meaning "love free of sensual desire" (1630s), which the word usually carries nowadays, is a Renaissance notion; it is based on Plato's writings in "Symposium" about the kind of interest Socrates took in young men, which originally had no reference to women. Related: Platonically.
Platonism (n.): 1560s, from Plato (see Platonic) + -ism.
Platonist (n.): 1540s, from Plato (see Platonic) + -ist.
platoon (n.): 1630s, from French peloton "platoon, group of people," from Middle French peloton (15c.), literally "little ball," hence, "agglomeration," diminutive of Old French pelote "ball" (see pellet).
platoon (v.): in baseball, "to alternate (a player) with another in the same position," 1967, from platoon (n.), which had been used in team sports since 1941.
Plattdeutsch: "Low German dialect of northern Germany," 1814, from German, from Dutch platduits, literally "flat (or low) German," from plat "flat, plain, clear" + duits "German" (see Dutch). In contrast to the speech of the upland parts of Germany.
platter (n.): late 13c., platere, from Anglo-French plater, from Old French plate "metal plate" (see plate (n.)).
platypus (n.): Australian duck-mole, 1799, from Modern Latin, from Greek platypous, literally "flat-footed," from platys "broad, flat" (see plaice (n.)) + pous "foot" (see foot).
Orig. the generic name, but, having already been given to a genus of beetles, it was in 1800 changed for Ornithorhyncus. [OED]
plaudit (n.): 1620s, short for plaudite "an actor's request for applause" (1560s), from Latin plaudite! "applaud!" second person plural imperative of plaudere "to clap, strike, beat; applaud, approve," of unknown origin (also in applaud, explode). This was the customary appeal for applause that Roman actors made at the end of a play. In English, the -e went silent then was dropped.
plausibility (n.): 1590s, from plausible + -ity.
plausible (adj.): 1540s, "acceptable, agreeable," from Latin plausibilis "deserving applause, acceptable," from plaus-, past participle stem of plaudere "to applaud" (see plaudit). Meaning "having the appearance of truth" is recorded from 1560s. Related: Plausibly.
play (v.): Old English plegan, plegian "move rapidly, occupy or busy oneself, exercise; frolic; make sport of, mock; perform music," from West Germanic *plegan "occupy oneself about" (cf. Old Saxon plegan "vouch for, take charge of," Old Frisian plega "tend to," Middle Dutch pleyen "to rejoice, be glad," German pflegen "take care of, cultivate"), from PIE root *dlegh- "to engage oneself," forming words in Celtic, Germanic, Slavic, and possibly Latin.

Meaning "to take part in a game" is from c.1200. Opposed to work (v.) since late 14c. Related: Played; playing. To play up "emphasize" is from 1909; to play down "minimize" is from 1930; to play along "cooperate" is from 1929. To play with oneself "masturbate" is from 1896; play for keeps is from 1861, originally of marbles or other children's games with tokens. To play second fiddle in the figurative sense is from 1809 ("Gil Blas"). To play into the hands (of someone) is from 1705. To play the _______ card is attested from 1886; to play fair is from mid-15c. To play (something) safe is from 1911; to play favorites is attested from 1902. For play the field see field (n.).
play (n.): Old English plega (West Saxon), plæga (Anglian) "quick motion; recreation, exercise, any brisk activity" (the latter sense preserved in swordplay, etc.), from or related to Old English plegan (see play (v.)). Meaning "dramatic performance" is attested by early 14c., perhaps late Old English. Meaning "free or unimpeded movement" of mechanisms, etc., is from c.1200. By early Middle English it could mean variously, "a game, a martial sport, activity of children, joke or jesting, revelry, sexual indulgence." Sporting sense "the playing of a game" first attested mid-15c.; sense of "specific maneuver or attempt" is from 1868. To be in play (of a hit ball, etc.) is from 1788. Play-by-play is attested from 1927. Play on words is from 1798. Play-money is attested from 1705 as "money won in gambling," by 1920 as "pretend money."
play-bill (n.): also playbill, 1670s, from play (n.) + bill (n.1).
play-day (n.): c.1600, from play + day.
play-dough (n.): 1959, from play + dough.