Online Etymology Dictionary

plan (n.): 1670s as a technical term in perspective drawing; 1706 as "drawing, sketch, or diagram of any object," from French plan "ground plan, map," literally "plane surface" (mid-16c.), from Latin planum "level or flat surface," noun use of adjective planus "level, flat" (see plane (n.1)). The notion is of "a drawing on a flat surface." Meaning "scheme of action, design" is first recorded 1706, possibly influenced by French planter "to plant," from Italian planta "ground plan."
plan (v.): 1728, "make a plan of," from plan (n.). Related: Planned; planning; plans. Planned economy is attested from 1931. Planned Parenthood (1942) formerly was Birth Control Federation of America.
planar (adj.): 1850, from Latin planaris "level, flat," from planum "plane" (see plane (n.1)).
Planaria (n.): flat worm-like animal, 1819, from Modern Latin (1776) noun use of fem. of Latin planarius, literally "on level ground" (here used to mean "flat"), from planum, planus "flat, level, even, plain" (see plane (n.1)). Related: Planarian.
planchet (n.): "metal disk out of which a coin is made," 1610s, from French planchette, literally "a small board," diminutive of Old French planche (12c.), from Latin planca "board, slab, plank" (see plank). The planchette used in automatism and on Ouija boards is a re-borrowing of the French word, 1860.
Planck: in physics, in reference to the work of German physicist Max Planck (1858-1947); such as Planck's constant, attested in English from 1901.
plane (n.1): "flat surface," c. 1600, from Latin planum "flat surface, plane, level, plain," noun use of neuter of adjective planus "flat, level, even, plain, clear," from PIE *pla-no- (source also of Lithuanian plonas "thin;" Celtic *lanon "plain;" perhaps also Greek pelanos "sacrificial cake, a mixture offered to the gods, offering (of meal, honey, and oil) poured or spread"), suffixed form of root *pele- (2) "to spread out; broad, flat" (source also of Old Church Slavonic polje "flat land, field," Russian polyi "open;" Old English and Old High German feld, Middle Dutch veld "field"). Introduced (perhaps by influence of French plan in this sense) to differentiate the geometrical senses from plain, which in mid-16c. English also meant "geometric plane." Figurative sense is attested from 1850. As an adjective from 1660s.
plane (n.2): 1908, short for aeroplane (see airplane).
plane (n.3): "tool for smoothing surfaces," mid-14c., from Old French plane, earlier plaine (14c.), from Late Latin plana, back-formation from planare "make level," from Latin planus "level, flat" (see plane (n.1)).
plane (n.4): "tree of the genus Platanus," late 14c., from Old French plane, earlier plasne (14c.), from Latin platanus, from Greek platanos, earlier platanistos "plane tree," a species from Asia Minor, associated with platys "broad" (see plaice (n.)), in reference to its leaves. Applied since 1778 in Scotland and northern England to the sycamore, whose leaves somewhat resemble those of the true plane tree.
plane (v.1): "to make smooth," early 14c., "to gloss over, explain away;" mid-14c. as "to make smooth or even," from Old French planer "to smooth, level off; wipe away, erase" (12c.), from Late Latin planare "make level," from Latin planus "level, flat" (see plane (n.1)). In early use in English often plain. Related: Planed; planing.
plane (v.2): "soar, glide on motionless wings," early 15c., from Old French planer "to hover (as a bird), to lie flat," from plan (n.) "plane," from Latin planum "flat surface" (see plane (n.1)), on notion of bird gliding with flattened wings. Of boats, etc., "to skim over the surface of water," it is first found 1913. Related: Planed; planing.
planet (n.): late Old English planete, from Old French planete (Modern French planète), from Late Latin planeta, from Greek planetes, from (asteres) planetai "wandering (stars)," from planasthai "to wander," of unknown origin, possibly from PIE *pele- (2) "flat, to spread" on notion of "spread out." So called because they have apparent motion, unlike the "fixed" stars. Originally including also the moon and sun; modern scientific sense of "world that orbits a star" is from 1630s.
planetarium (n.): 1734, "orrery," Modern Latin, from Late Latin planeta (see planet) + Latin -arium "a place for." Sense of "device for projecting the night sky onto the interior of a dome" is attested from 1929.
planetary (adj.): 1590s; see planet + -ary. Probably from Late Latin planetarius "pertaining to a planet or planets," but this is attested only as "an astrologer." Planetary nebula, so called for its shape, attested from 1785.
plangent (adj.): "beating with a loud sound," 1822, from Latin plangentem (nominative plangens), present participle of plangere "to strike, beat" (see plague (n.)). Related: Plangently.
plani-: word-forming element meaning "level, plane," from Latin plani-, from planus "flat, level" (see plane (n.1)).
planisphere (n.): late 14c., from Medieval Latin planisphaerium, from Latin planus (see plane (n.1)) + sphaera (see sphere (n.)).
plank (n.): late 13c. (c. 1200 as a surname), from Old North French planke, variant of Old French planche "plank, slab, little wooden bridge" (12c.), from Late Latin planca "broad slab, board," probably from Latin plancus "flat, flat-footed," from PIE *plak- (1) "to be flat" (see placenta). Technically, timber sawed to measure 2 to 6 inches thick, 9 inches or more wide, and 8 feet or more long. Political sense of "item of a party platform" is U.S. coinage from 1848. To walk the plank, supposedly a pirate punishment, is first attested 1789 and most early references are to slave-traders disposing of excess human cargo in crossing the ocean.
planktology (n.): 1892, from German planktologie (1891); see plankton + -logy. The native formation planktonology (1896) is less common.
plankton (n.): 1891, from German Plankton (1887), coined by German physiologist Viktor Hensen (1835-1924) from Greek plankton, neuter of planktos "wandering, drifting," verbal adjective from plazesthai "to wander, drift," from plazein "to drive astray," from PIE root *plak- (2) "to strike, hit" (see plague (n.)). Related: Planktonic.
planner (n.): 1716, "one who plans," agent noun from plan (v.). Derogatory variant planster attested from 1945. Meaning "book or device that enables one to plan" is from 1971.
planning (n.): 1748, verbal noun from plan (v.).
plano-: alternative form of Latin plani- "flat, level," but also used in sciences as a comb. form of Greek planos "wandering" (see planet).
plant (n.): Old English plante "young tree or shrub, herb newly planted," from Latin planta "sprout, shoot, cutting" (source of Spanish planta, French plante), perhaps from *plantare "to drive in with the feet, push into the ground with the feet," from planta "sole of the foot," from nasalized form of PIE *plat- "to spread, flat" (see place (n.)).

Broader sense of "any vegetable life, vegetation generally" is first recorded 1550s. Most extended usages are from the verb, on the notion of "something planted;" such as "construction for an industrial process," 1789, at first with reference to the set-up of machinery, later also the building; also slang meaning "a spy" (1812). Many of these follow similar developments in the French form of the word. German Pflanz, Irish cland, Welsh plant are from Latin.
plant (v.): "put in the ground to grow," Old English plantian, from Latin plantare (see plant (n.)). Reinforced by cognate Old French planter. Without reference to growing, "to insert firmly," late 14c. Of colonies from c. 1300. Figuratively, of ideas, etc., from early 15c. Meaning "to bury" is U.S. slang from U.S., 1855. Related: Planted; planting.
plantain (n.1): "banana," 1550s, plantan, from Spanish plátano, plántano, probably from Carib palatana "banana" (Arawak pratane), and altered by association with Spanish plátano "plane tree," from Medieval Latin plantanus "plane tree," itself altered (by association with Latin planta "plant") from Latin platanus (see plane (n.4)). So called from the shape of its leaves. There is no similarity or relation between this plant and plantain (n.2).
plantain (n.2): "weed of the genus Plantago," mid-13c., from Anglo-French plaunteyne, Old French plantain, from Latin plantaginem (nominative plantago), the common weed, from planta "sole of the foot" (see plant (n.)); so called from its flat leaves.
plantar (adj.): 1706, from Latin plantaris "pertaining to the sole of the foot," from planta "sole of the foot" (see plant (n.)).
plantation (n.): mid-15c., "action of planting," from Middle French plantation, from Latin plantationem (nominative plantatio) "a planting," noun of action from past participle stem of plantare "to plant" (see plant). Historically used for "colony, settlement in a new land" (1610s); meaning "large farm on which tobacco or cotton is grown" is first recorded 1706.
planter (n.): "one who sows seeds," late 14c., agent noun from plant (v.). Mechanical sense by 1850. Meaning "proprietor of a cultivated estate in West Indies or southern colonies of North America" is from 1640s, hence planter's punch (1924). Meaning "a pot for growing plants" recorded by 1959.
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" (compare 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 (n.): "small puddle, shallow pool, wet ground," Old English plæsc "pool of water, puddle," probably imitative (compare Dutch plass "pool"). Meaning "noise made by splashing" is first recorded 1510s.
plash (v.1): "to splash," 1580s, from plash (n.) and also imitative (compare Dutch plassen, German platschen). Related: Plashed; plashing.
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 (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.
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).