plenum (n.) Look up plenum at Dictionary.com
1670s, "filled space" (opposite of vacuum), from Latin plenum (spatium) "full (space)," neuter of adjective plenus "complete, full" (see plenary). The meaning "of a full assembly of legislators" is first recorded 1772.
pleo- Look up pleo- at Dictionary.com
see pleio-.
pleomorphic (adj.) Look up pleomorphic at Dictionary.com
"having more than one form," 1886, from pleo- + -morphe "form" (see Morpheus). Related: Pleomorphism.
pleonasm (n.) Look up pleonasm at Dictionary.com
"redundancy in words," 1580s, from Late Latin pleonasmus, from Greek pleonasmos, from pleonazein "to be more than enough, to be superfluous," in grammatical use, "to add superfluously," from comb. form of pleon "more" (see pleio-).
pleonastic (adj.) Look up pleonastic at Dictionary.com
1778, with -ic + Greek pleonastos "abundant," from pleonazein (see pleonasm). Related: Pleonastical (1650s).
plesiosaurus (n.) Look up plesiosaurus at Dictionary.com
1825, from Modern Latin Pleisiosaurus (1821), coined by English paleontologist William Daniel Conybeare (1787-1857) from Greek plesios "near," related to pelas, + -saurus.
plethora (n.) Look up plethora at Dictionary.com
1540s, a medical word for "excess of body fluid," from Late Latin plethora, from Greek plethore "fullness," from plethein "be full" (see pleio-). Figurative meaning "too-muchness, overfullness in any respect" is first recorded 1700. Related: Plethoric.
pleura (n.) Look up pleura at Dictionary.com
early 15c., medical Latin, from Greek pleura "side of the body, rib," also "flank of an army, page of a book," of unknown origin.
pleural (adj.) Look up pleural at Dictionary.com
1835, from pleura + -al (1). Alternative pleuric is attested from 1825.
pleurisy (n.) Look up pleurisy at Dictionary.com
late 14c., from Old French pleurisie (13c., Modern French pleurésie) and directly from Late Latin pleurisis "pleurisy," alteration of Latin pleuritis "pain in the side," from Greek pleuritis, from pleura "side of the body, rib," of unknown origin. Spelling altered in Late Latin on model of Latin stem plur- "more" (as in Medieval Latin pluritas "multitude"), as if in reference to "excess of humors."
pleuro- Look up pleuro- at Dictionary.com
before vowels pleur-, word-forming element meaning "pertaining to the side; pertaining to the pleura," from comb. form of Greek pleura (see pleura).
plex Look up plex at Dictionary.com
in various usages, from Latin plex-, past participle stem of plectere "to plait" (see complex (adj.)).
Plexiglas (n.) Look up Plexiglas at Dictionary.com
1935, proprietary name (Röhm & Haas) for a substance also sold as Perspex and Lucite. Often written incorrectly as plexiglass.
plexus (n.) Look up plexus at Dictionary.com
1680s, Modern Latin, literally "braid, network," noun use of past participle of Latin plectere "to twine, braid, fold" (see complex (adj.)); used of a network, such as solar plexus "network of nerves in the abdomen" (see solar). Related: Plexal.
pliable (adj.) Look up pliable at Dictionary.com
late 14c., from Old French ploiable "flexible, bendable," from plier "to bend" (see ply (n.)). Related: Pliably, pliability.
pliant (adj.) Look up pliant at Dictionary.com
late 14c., from Old French ploiant "bending, supple; compliant, fickle," as a noun, "turncoat" (13c.), present participle of ploier "to bend" (see ply (n.)). Figurative sense of "easily influenced" is from c.1400. Related: Pliancy.
plie (n.) Look up plie at Dictionary.com
in ballet, 1892, from French plié, from plier literally "to bend," from Old French ploier (see ply (n.)).
plier (n.) Look up plier at Dictionary.com
"one who folds," 1670s, agent noun from ply (v.).
pliers (n.) Look up pliers at Dictionary.com
"pincers," 1560s, plural agent noun from ply (n.). French cognate plieur meant "folder."
plight (v.) Look up plight at Dictionary.com
"to pledge" (obsolete except in archaic plight one's troth), from Old English pligtan, plihtan "to endanger, imperil, compromise," verb form of pliht (n.) "danger, risk" (see plight (n.2)). Related: Plighted; plighting.
plight (n.1) Look up plight at Dictionary.com
"condition or state (usually bad)," late 12c., "danger, harm, strife," from Anglo-French plit, pleit, Old French pleit, ploit "condition" (13c.), originally "way of folding," from Vulgar Latin *plictum, from Latin plicitum, neuter past participle of Latin plicare "to fold, lay" (see ply (v.1)).

Originally in neutral sense (as in modern French en bon plit "in good condition"), sense of "harmful state" (and current spelling) probably is from convergence and confusion with plight (n.2) via notion of "entangling risk, pledge or promise with great risk to the pledger."
plight (n.2) Look up plight at Dictionary.com
"pledge," mid-13c., "pledge, promise," usually involving risk or loss in default, from Old English pliht "danger, risk, peril, damage," from Proto-Germanic *pleg- (cognates: Old Frisian plicht "danger, concern, care," Middle Dutch, Dutch plicht "obligation, duty," Old High German pfliht, German Pflicht "obligation, duty" (see plight (v.)). Compare Old English plihtere "look-out man at the prow of a ship," plihtlic "perilous, dangerous."
Plimsoll (n.) Look up Plimsoll at Dictionary.com
"mark on the hull of a British ship showing how deeply she may be loaded," 1881, from Samuel Plimsoll (1824-1898), M.P. for Derby and advocate of shipping reforms (which were embodied in the Merchant Shipping Act of 1876). Sense extended 1907 to "rubber-soled canvas shoe" (equivalent of American English sneakers) because the band around the shoes that holds the two parts together reminded people of a ship's Plimsoll line; sense perhaps reinforced by sound association with sole (which sometimes influenced the spelling to plimsole). The name is of Huguenot origin.
plink (v.) Look up plink at Dictionary.com
1941, imitative. As a noun from 1954. Related: Plinked; plinking.
plinth (n.) Look up plinth at Dictionary.com
1610s, from French plinthe (16c.) and directly from Latin plinthus, from Greek plinthos "brick, squared stone," cognate with Old English flint (see flint).
plio- Look up plio- at Dictionary.com
word-forming element, Latinate form of pleio-.
Pliocene (adj.) Look up Pliocene at Dictionary.com
1833, from plio- "more" (Latinized form of pleio-) + -cene.
PLO Look up PLO at Dictionary.com
initialism (acronym) of Palestinian Liberation Organization, by 1965.
plod (v.) Look up plod at Dictionary.com
1560s, of uncertain origin, perhaps imitative of the sound of walking heavily or slowly. Related: Plodded; plodding.
plodding (adj.) Look up plodding at Dictionary.com
"diligent and dull," 1580s, present participle adjective from plod (v.).
plonk (v.) Look up plonk at Dictionary.com
1874, imitative. From 1903 as a noun. Related: Plonked; plonking.
plop (v.) Look up plop at Dictionary.com
1821, imitative of the sound of a smooth object dropping into water. Related: Plopped; plopping. Thackary (mid-19c.) used plap (v.). As a noun from 1833.
plosive (n.) Look up plosive at Dictionary.com
type of consonantal sound, 1899, from explosive. As an adjective from 1909.
plot (v.) Look up plot at Dictionary.com
1580s, "to lay plans for" (usually with evil intent); 1590s in the literal sense of "to make a map or diagram," from plot (n.). Related: Plotted; plotter; plotting.
plot (n.) Look up plot at Dictionary.com
Old English plot "small piece of ground," of unknown origin. Sense of "ground plan," and thus "map, chart" is 1550s; that of "a secret, plan, scheme" is 1580s, probably by accidental similarity to complot, from Old French complot "combined plan," of unknown origin, perhaps a back-formation from compeloter "to roll into a ball," from pelote "ball." Meaning "set of events in a story" is from 1640s. Plot-line (n.) attested from 1957.
plough Look up plough at Dictionary.com
alternative spelling of plow. Related: Ploughed; ploughing.
plover (n.) Look up plover at Dictionary.com
c.1300, from Anglo-French plover, Old French pluvier, earlier plovier (c.1200), from Vulgar Latin *plovarius, literally "belonging to rain," from Latin pluvia "rain (water)" from pluere "to rain," from PIE root *pleu- "to flow" (see pluvial). Perhaps so called because the birds' migration arrival coincides with the start of the rainy season, or from its supposed restlessness when rain approaches.
plow (n.) Look up plow at Dictionary.com
late Old English plog, ploh "plow; plowland" (a measure of land equal to what a yoke of oxen could plow in a day), possibly from a Scandinavian source (such as Old Norse plogr "plow," Swedish and Danish plog), from Proto-Germanic *plogo- (cognates: Old Saxon plog, Old Frisian ploch "plow," Middle Low German ploch, Middle Dutch ploech, Dutch ploeg, Old High German pfluog, German Pflug), a late word in Germanic, of uncertain origin. Old Church Slavonic plugu, Lithuanian plugas "plow" are Germanic loan-words, as probably is Latin plovus, plovum "plow," a word said by Pliny to be of Rhaetian origin.

Replaced Old English sulh, cognate with Latin sulcus "furrow" (see sulcus). As a name for the star pattern also known as the Big Dipper or Charles's Wain, it is attested by early 15c., perhaps early 14c. The three "handle" stars (in the Dipper configuration) generally are seen as the team of oxen pulling the plow, though sometimes they are the handle.
plow (v.) Look up plow at Dictionary.com
late 14c., from plow (n.). Transferred sense from 1580s. Related: Plowed; plowing.
plow-boy (n.) Look up plow-boy at Dictionary.com
also plowboy, 1560s, from plow + boy.
plowman (n.) Look up plowman at Dictionary.com
also plow-man, c.1300, from plow + man (n.).
plowshare (n.) Look up plowshare at Dictionary.com
late 14c., from plow + share (n.2). To beat swords into plowshares is from Isaiah ii:4.
ploy (n.) Look up ploy at Dictionary.com
1722, "anything with which one amuses oneself," Scottish and northern England dialect, possibly a shortened form of employ or deploy. Popularized in the sense "move or gambit made to gain advantage" by British humorist Stephen Potter (1900-1969).
pluck (n.) Look up pluck at Dictionary.com
c.1400, "act of plucking," from pluck (v.). Meaning "courage, boldness" (1785), originally in pugilism slang, is a figurative use from earlier meaning "heart, viscera" (1610s) as that which is "plucked" from slaughtered livestock. Perhaps influenced by figurative use of the verb in pluck up (one's courage, etc.), attested from c.1300.
pluck (v.) Look up pluck at Dictionary.com
late Old English ploccian, pluccian "pull off, cull," from West Germanic *plokken (cognates: Middle Low German plucken, Middle Dutch plocken, Dutch plukken, Flemish plokken, German pflücken), perhaps from Vulgar Latin *piluccare (source of Old French peluchier, late 12c.; Italian piluccare), a frequentative, ultimately from Latin pilare "pull out hair," from pilus "hair" (see pile (n.3)). But despite the similarities, OED finds difficulties with this and cites gaps in historical evidence. Related: Plucked; plucking.
To pluck a rose, an expression said to be used by women for going to the necessary house, which in the country usually stands in the garden. [F. Grose, "Classical Dictionary of the Vulgar Tongue," 1785]
This euphemistic use is attested from 1610s. To pluck up "summon up" is from c.1300.
plucky (adj.) Look up plucky at Dictionary.com
1831, from pluck (n.) + -y (2). Related: Pluckily; pluckiness.
plug (v.) Look up plug at Dictionary.com
"close tightly (a hole), fill," 1620s, from plug (n.) or from Dutch pluggen. Meaning "work energetically at" is c.1865. Sense of "popularize by repetition" is from 1906. Slang sense "put a bullet into" is recorded from 1870. Related: Plugged; plugging.
plug (n.) Look up plug at Dictionary.com
1620s, originally a seamen's term, probably from Dutch plug, Middle Dutch plugge "bung, stopper," related to Norwegian plugg, Danish pløg, North Frisian plaak, Middle Low German pluck, German Pflock; ultimate origin uncertain. Irish and Gaelic words are from English. Sense of "wad or stick of tobacco" is attested from 1728, based on resemblance. Electrical sense is from 1883, based on being inserted; meaning "sparking device in an internal combustion engine" is from 1886. Meaning "advertisement" first recorded 1902, American English, perhaps from verb sense "work energetically at" (c.1865).
plug-in (adj.) Look up plug-in at Dictionary.com
1922, from plug (v.) + in (adv.).
plug-ugly (n.) Look up plug-ugly at Dictionary.com
"ruffian," 1856, originally in Baltimore, Maryland, from plug (n.), American English slang name for the stovepipe hats then popular among young men, + ugly.