Online Etymology Dictionary

plump (adj.): late 15c., "blunt, dull" (in manners), from Dutch plomp "blunt, thick, massive, stumpy," probably related to plompen "fall or drop heavily" (see plump (v.)). Meaning "fleshy, of rounded form" is from 1540s in English. Danish and Swedish plump "rude, coarse, clumsy" are from the Low German word and represent a different sense development.
plump (v.1): c. 1300, "to fall or strike with a full impact," common Low German word, from or related to Middle Dutch and Dutch plompen, East Frisian plumpen, Middle Low German plumpen, probably more or less imitative of something hard striking something soft. Hence plump (n.) "a firm blow," in pugilism usually one to the stomach.
To plump; to strike, or shoot. I'll give you a plump in the bread basket, or the victualling office; I'll give you a blow in the stomach. [Grose, "Dictionary of the Vulgar Tongue," London, 1785]

Or, even if any of them should suspect me, I know how to bring myself off. It is but pretending to be affronted, stripping directly, challenging him to fight, and before he can be on his guard, hitting him a plump in the bread-basket, that shall make him throw up his accounts; and I'll engage he will have but very little stomach to accuse me after. ["The Reverie: or A Flight to the Paradise of Fools," London, 1763]
plump (v.2): "to become plump," 1530s, from plump (adj.). Meaning "to plump (something) up, to cause to swell" is from 1530s. Related: Plumped; plumping.
plumpness (n.): 1540s, from plump (adj.) + -ness.
plunder (v.): 1630s, from German plündern, from Middle High German plunderen "to plunder," originally "to take away household furniture," from plunder (n.) "household goods, clothes," also "lumber, baggage" (14c.; compare Modern German Plunder "lumber, trash"), which is related to Middle Dutch plunder "household goods;" Frisian and Dutch plunje "clothes." A word acquired by English via the Thirty Years War and applied in native use after the outbreak of the English Civil War in 1642. Related: Plundered; plundering. Plunderbund was a U.S. colloquial word from 1914 referring to "a corrupt alliance of corporate and financial interests," with German Bund "alliance, league."
plunder (n.): "goods taken by force; act of plundering," 1640s, from plunder (v.).
plunge (v.): late 14c., "to put or thrust violently into," also intransitive, from Old French plongier "plunge, sink into; plunge into, dive in" (mid-12c., Modern French plonger), from Vulgar Latin *plumbicare "to heave the lead," from Latin plumbum "lead" (see plumb (n.)). Original notion perhaps is of a sounding lead or a fishing net weighted with lead. Related: Plunged; plunging. Plunging neckline attested from 1949.
plunge (n.): c. 1400, "deep pool," from plunge (v.). From late 15c. as "a sudden pitch forward;" meaning "act of plunging" is from 1711. Figurative use in take the plunge "commit oneself" is from 1845, from earlier noun sense of "point of being in trouble or danger" (1530s).
plunger (n.): 1610s, "one who plunges," agent noun from plunge (v.). As a mechanism, 1777.
plunk (v.): 1805, "to pluck a stringed instrument;" 1808 in sense of "drop down abruptly;" 1888 as "to hit, wound, shoot." Probably of imitative origin in all cases. Related: Plunked; plunking.
pluperfect (adj.): 1520s, shortened from Latin (tempus praeteritum) plus (quam) perfectum "(past tense) more (than) perfect." Translates Greek khronos hypersyntelikos. See plus and perfect (adj.).
plural (adj.): late 14c., from Old French plurel "more than one" (12c., Modern French pluriel), from Latin pluralis "of or belonging to more than one," from plus (genitive pluris) "more" (see plus). The noun meaning "a plural number" is from late 14c.
pluralism (n.): 1818, as a term in church administration, from plural + -ism. Attested from 1882 as a term in philosophy for a theory which recognizes more than one ultimate principle. In political science, attested from 1919 (in Harold J. Laski) in sense "theory which opposes monolithic state power." General sense of "toleration of diversity within a society or state" is from 1933. Related: Pluralist (1620s, in the church sense); pluralistic.
plurality (n.): late 14c., "state of being plural," from Old French pluralite (14c.), from Late Latin pluralitatem (nominative pluralitas), from Latin pluralis (see plural). Meaning "fact of there being many, multitude" is from mid-15c. Church sense of "holding of two or more offices concurrently" is from mid-14c. Meaning "greater number, more than half" is from 1570s but is etymologically improper, perhaps modeled on majority. U.S. sense of "excess of votes over rival candidate(s)," especially when none has an absolute majority, is from 1828.
pluri-: word-forming element meaning "more than one, several, many," from Latin pluri-, from stem of plus (genitive pluris); see plus.
pluripotential (adj.): 1925, from pluri- + potential. Related: Pluripotent; pluripotency.
plus (n.): 1570s, the oral rendering of the arithmetical sign +, from Latin plus "more, in greater number, more often" (comparative of multus "much"), altered (by influence of minus) from *pleos, from PIE *pele- (1) "to fill" (see poly-).

As a preposition, between two numbers to indicate addition, from 1660s. [Barnhart writes that this sense "did not exist in Latin and probably originated in commercial language of the Middle Ages."] Placed after a whole number to indicate "and a little more," it is attested from 1902. As a conjunction, "and," it is American English colloquial, attested from 1968. As a noun meaning "an advantage" from 1791. Plus fours (1921) were four inches longer in the leg than standard knickerbockers, to produce an overhang, originally a style associated with golfers. The plus sign itself has been well-known since at least late 15c. and is perhaps an abbreviation of Latin et (see et cetera).
plus ca change: 1903, French, plus ça change, plus c'est la même chose (1849), literally "the more it changes, the more it stays the same."
plush (n.): "soft fabric," 1590s, from Middle French pluche "shag, plush," contraction of peluche "hairy fabric," from Old French peluchier "to pull, to tug, to pluck" (the final process in weaving plush), from Vulgar Latin *piluccare "remove hair" (see pluck (v.)). Related: Plushy; plushness.
plush (adj.): "swank, luxurious," 1927, from plush (n.). Plushy in this sense is recorded from 1923. Related: Plushly; plushness.
plutarchy (n.): "plutocracy," 1640s, from Greek ploutos "wealth" (see Pluto) + -archy.
Pluto (n.): Roman god of the underworld, from Latin Pluto, Pluton, from Greek Plouton "god of wealth," literally "wealth, riches," probably originally "overflowing," from PIE *pleu- "to flow" (see pluvial). The alternative Greek name of Hades in his function as the god of wealth (precious metals and gems, coming from beneath the earth, form part of his realm). The planet (since downgraded) was discovered 1930 by C.W. Tombaugh; Minerva also was suggested as a name for it. The cartoon dog first appeared in Walt Disney's "Moose Hunt," released April 1931.
plutocracy (n.): 1650s, from Greek ploutokratia "rule or power of the wealthy or of wealth," from ploutos "wealth" (see Pluto) + -kratia "rule" (see -cracy). Synonym plutarchy is slightly older (1640s). Pluto-democracy "plutocracy masquerading as democracy" is from 1895.
plutocrat (n.): "person who rules by his wealth," 1838, back-formation from plutocracy. Related: Plutocratic (1843); plutocratical (1833).
plutogogue (n.): "spokesman for plutocrats," 1894, from Greek ploutos "wealth" + ending from demagogue.
plutolatry (n.): "worship of wealth," 1889, from Greek ploutos "wealth" (see Pluto) + -latry. Related: Plutolater.
plutomania (n.): 1650s, "mad pursuit of wealth," from Greek ploutos "wealth" (see Pluto) + mania. As "imaginary possession of wealth" from 1894. Related: Plutomaniac.
Plutonian (adj.): 1660s, "pertaining to the god Pluto," from Latin Plutonius, from Greek Ploutonius, from Plouton "pertaining to Pluto" (see Pluto). Geological sense is from 1828 (see plutonic). Planetary sense by 1952.
plutonic (adj.): "pertaining to or involving intense heat deep in the earth's crust," 1796, coined by Irish scientist Richard Kirwin (1733-1812) from comb. form of Pluto (as god of the underworld) + -ic. Especially in reference to early 19c. geological theory (championed by Hutton) that attributed most of the earth's features to action of internal heat, a theory which triumphed over its rival, neptunism, which attributed them to water. Related: Plutonism; Plutonist.
plutonium (n.): transuranic element, 1942, from Pluto, the planet, + element ending -ium. Discovered at University of California, Berkeley, in 1941, the element named on suggestion of Seaborg and Wahl because it follows neptunium in the periodic table as Pluto follows Neptune in the Solar System. The name plutonium earlier had been proposed for barium and was sometimes used in this sense early 19c.
plutonomic (adj.): "of or pertaining to the science or study of wealth or riches," 1853, from comb. form of Greek ploutos "wealth" (see Pluto) + ending from economic. Fell from currency 1870s, revived 1990s. Related: Plutonomics (1991); plutonomist (1869).
pluvial (adj.): 1650s, "pertaining to rain," from French pluvial (12c.), from Latin pluvialis "pertaining to rain, rainy, rain-bringing," from (aqua) pluvia "rain (water)," from fem. of pluvius "rainy," from plovere "to rain," from PIE root *pleu- "to flow, to swim" (source also of Sanskrit plavate "navigates, swims;" Greek plynein "to wash," plein "to navigate," ploein "to float, swim," plotos "floating, navigable;" Armenian luanam "I wash;" Old English flowan "to flow;" Old Church Slavonic plovo "to flow, navigate;" Lithuanian pilu, pilti "to pour out," plauju, plauti "to swim, rinse").
ply (v.1): "work with, use," late 14c., shortened form of applien "join to, apply" (see apply). The core of this is Latin plicare "to lay, fold, twist," from PIE root *plek- "to plait, twist" (source also of Greek plekein "to plait, twine," plektos "twisted;" Latin plectere (past participle plexus) "to plait, braid, intertwine;" Old Church Slavonic plesti "to braid, plait, twist;" Gothic flahta "braid;" Old English fleax "cloth made with flax, linen").

Sense of "travel regularly" is first 1803, perhaps from earlier sense "steer a course" (1550s). Related: Plied; plies; plying.
ply (n.): "a layer, a fold" 1530s, from Middle French pli "a fold" (13c.), alteration of Old French ploi "fold, pleat, layer" (12c.), verbal noun from ployer (later pleier) "to bend, to fold," from Latin plicare "to fold, lay" see ply (v.1)). This is the ply in plywood.
ply (v.2): "to bend," late 14c., plien, from Old French plier, earlier pleier "to fold, bend," from Latin plicare "to lay, fold, twist" (see ply (v.1)). Related: Plied; plies; plying.
Plymouth: city in Devon, England, named for its location at the mouth of the Plym River; the river is in turn named for Plympton, literally "plum-tree farm." Earlier Plymouth was Sutton Prior. The town in Massachusetts, U.S., was named 1620 by immigrants on the "Mayflower," which had sailed from Plymouth, England, and landed at what became known as Plymouth Rock.
plywood (n.): 1907, from ply (n.) + wood (n.). So called because the layers are arranged so that the grain of one runs at right angles to that of the next.
pn-: consonant sound in some English words derived from Greek. The p- typically is silent in English but pronounced in French, German, Spanish, etc.
pneuma (n.): used in English in various sense, from Greek pneuma "a blowing, a wind, blast; breeze; influence; breathed air, breath; odor, scent; spirit of a person; inspiration, a spirit, ghost," from pnein "to blow, to breathe," from PIE root *pneu- "to breathe," of imitative origin (compare Greek pnoe "breath," pnoia "breathing;" Old English fnora "sneezing," fnæran "to snort").
pneumatic (adj.): 1650s, from Latin pneumaticus "of the wind, belonging to the air," from Greek pneumatikos "of wind or air" (which is attested mainly as "of spirit, spiritual"), from pneuma (genitive pneumatos) "the wind," also "breath" (see pneuma). Earlier was pneumatical (c. 1600).
pneumatics (n.): 1650s, from pneumatic. Also see -ics.
pneumato-: before vowels pneumat-, word-forming element meaning "wind, air, spirit, presence of air," from comb. form of Greek pneuma (genitive pneumatos); see pneuma.
pneumo-: before vowels pneum-, word-forming element meaning "lung," from comb. form of Greek pneumon (see pneumonia).
pneumonia (n.): c. 1600, from Modern Latin, from Greek pneumonia "inflammation of the lungs," from pneumon "lung," altered (perhaps by influence of pnein "to breathe") from pleumon "lung," literally "floater," probably cognate with Latin pulmo (see pulmonary), from PIE *pleu- "to flow, to swim" (see pluvial). Alteration in Greek perhaps by influence of pnein "to breathe."
pneumonic (adj.): "pertaining to the lungs," 1670s, from Latin pneumonicus, from Greek pneumonikos "of the lungs," from pneumon (see pneumonia).
pneumono-: before vowels pneumon-, word-forming element meaning "lung," from comb. form of Greek pneumon (genitive pneumonos "lung" (see pneumonia).
pneumonoultramicroscopicsilicovolcanoconiosis (n.): 1962, "A facetious word alleged to mean 'a lung disease caused by the inhalation of very fine silica dust' but occurring chiefly as an instance of a very long word" [OED]. Said in an early reference to have been invented by seventh grade students in Norfolk, Virginia.
pneumothorax (n.): 1821, from French pneumothorax (1803), coined by French physician Jean Marc Gaspard Itard (1774-1838) from Greek pneumon (see pneumonia) + thorax.
Po: large river in northern Italy, from Latin Padus, a name of Celtic origin.
po-face (adj.): "expressionless, impassive," 1934, American English, of unknown origin.