polonium (n.) Look up polonium at Dictionary.com
radioactive element, 1898, discovered by Marie Curie (nee Skłodowska), 1867-1934, and her husband, and named for her native country, Poland (Modern Latin Polonia). With element-name ending -ium.
poltergeist (n.) Look up poltergeist at Dictionary.com
1838, from German Poltergeist, literally "noisy ghost," from poltern "make noise, rattle" (from PIE root *bhel- (4) "to sound, ring, roar;" source of bellow, bell) + Geist "ghost" (see ghost (n.)). In the native idiom of Northern England, such phenomenon likely would be credited to a boggart.
poltroon (n.) Look up poltroon at Dictionary.com
"A coward; a nidgit; a scoundrel" [Johnson, who spells it poltron], 1520s, from Middle French poultron "rascal, coward" (16c., Modern French poltron), from Italian poltrone "lazy fellow, coward," apparently from *poltro "couch, bed" (compare Milanese polter, Venetian poltrona "couch"), perhaps from a Germanic source (compare Old High German polstar "pillow;" see bolster (n.)). Also see -oon.
poly- Look up poly- at Dictionary.com
word-forming element meaning "many, much, multi-, one or more," from Greek poly-, combining form of polys "much" (plural polloi); cognate with Latin plus, from PIE root *pele- (1) "to fill," with derivatives referring to multitudinousness or abundance (cognates: Sanskrit purvi "much," prayah "mostly;" Avestan perena-, Old Persian paru "much;" Greek plethos "people, multitude, great number," polys "much, plenty," ploutos "wealth;" Lithuanian pilus "full, abundant;" Old Church Slavonic plunu; Gothic filu "much," Old Norse fjöl-, Old English fela, feola "much, many;" Old English folgian; Old Irish lan, Welsh llawn "full;" Old Irish il, Welsh elu "much"); probably related to root *pele- (2) "to spread."

Properly used in compounds only with words of Greek origin. In chemical names, usually indicating a compound with a large number of atoms or molecules of the same kind (such as polymer).
polyamorous (adj.) Look up polyamorous at Dictionary.com
by 1972, from poly- + amorous. Related: Polyamory.
polyandria (n.) Look up polyandria at Dictionary.com
1751 in botany; 1809 of human relationships, from poly- "many" andr-, stem of aner "man, husband" (see anthropo-) + -ia "condition of." Late Greek polyandria meant "populousness."
polyandrous (adj.) Look up polyandrous at Dictionary.com
1764, in botany, "having numerous stamens," from poly- + stem of aner "man, husband" (see anthropo-). From 1854 of humans, "having more than one husband." Greek polyandros meant "numerous" (of persons), "populous" (of places); polyanor meant "of many husbands."
polyandry (n.) Look up polyandry at Dictionary.com
1767, nativized form of polyandria. Related: Polyandrist.
polycentric (adj.) Look up polycentric at Dictionary.com
1826, from poly- + centric.
polychrome (adj.) Look up polychrome at Dictionary.com
"having many colors," 1816, from French polychrome, from Latinized form of Greek polykhromos "many-colored" (see poly- + chrome). As a noun from 1800. Related: Polychromic; polychromatic; polychromate.
polyclinic (n.) Look up polyclinic at Dictionary.com
"place for treatment of various diseases," 1890, from poly- "many" + clinic.
polydactyl (n.) Look up polydactyl at Dictionary.com
1894, from French polydactyle (adj.) "having more fingers and toes than is usual," from Greek polydaktylos; see poly- + dactyl. As an adjective from 1874. Related: Polydactyly; polydactylism (1868).
polydipsia (n.) Look up polydipsia at Dictionary.com
"excessive thirst," 1650s, from Greek polydipsios "very thirsty," from poly- (see poly-) + dipsa "thirst" + -ia "condition of."
Polydorus Look up Polydorus at Dictionary.com
Priam's youngest son (Homer), from Latin Polydorus, from Greek Polydoros "one who has received many gifts," noun use of adjective meaning "richly endowed," from polys "much, many" (see poly-) + doron "gift" (see date (n.1)).
polyester (n.) Look up polyester at Dictionary.com
1929, formed from polymer + ester. Polyester fiber was discovered 1941.
polyethylene (n.) Look up polyethylene at Dictionary.com
polymer of ethylene, 1862, from French polyéthylène; see poly- + ethylene. Related: Polyethylenic (1860).
polygamous (adj.) Look up polygamous at Dictionary.com
1610s, from polygamy + -ous, or else from Late Greek polygamos "often married." Related: Polygamously.
polygamy (n.) Look up polygamy at Dictionary.com
1590s, from Late Latin polygamia, from Late Greek polygamia "polygamy," from polygamos "often married," from polys "many" + gamos "marriage" (see gamete). Not etymologically restricted to marriage of one man and multiple women (technically polygyny), but often used as if it were. Related: Polygamist.
polygenesis (n.) Look up polygenesis at Dictionary.com
"plurality of origins," 1858, from poly- + -genesis "birth, origin, creation." Related: Polygenetic (1851).
polygenic (adj.) Look up polygenic at Dictionary.com
1823, from poly- + -genic. Used in chemistry from 1873 for "forming two or more compounds" (with hydrogen or another univalent element). Related: Polygenetic.
polygenous (adj.) Look up polygenous at Dictionary.com
"composed of many kinds," 1797; see poly- + genus.
polyglot (adj.) Look up polyglot at Dictionary.com
1650s, from Greek polyglottos "speaking many languages," literally "many-tongued," from polys "many" (see poly-) + glotta, Attic variant of glossa "language," literally "tongue" (see gloss (n.2)). As a noun from 1640s.
polygon (n.) Look up polygon at Dictionary.com
1570s, from Latin polygonum, from Greek polygonon, noun use of neuter of adjective polygonos "many-angled," from polys "many" (see poly-) + -gonos "angled," from gonia "angle" (see -gon). Related: Polygonal.
polygraph (n.) Look up polygraph at Dictionary.com
1794, "mechanical device for making multiple copies of something written or drawn," from Greek polygraphos "writing much," from polys "much" (see poly-) + graphos "writing," from graphein "to write" (see -graphy).

Meaning "instrument for recording several pulsations of the body at the same time" is 1871; first used as a lie detector 1921. Related: Polygraphy (1590s); polygraphic (1771).
polygyny (n.) Look up polygyny at Dictionary.com
1780, "condition of having many wives," from poly- "many" (see poly-) + Greek gyne "woman, wife" (see queen). Related: Polygynous.
polyhedral (adj.) Look up polyhedral at Dictionary.com
1741, from polyhedron + -al (1).
polyhedron (n.) Look up polyhedron at Dictionary.com
1560s, from Latinized form of Greek polyedron, neuter of adjective polyedros "having many bases or sides," from polys "many" (see poly-) + hedra "seat, base, chair, face of a geometric solid," from PIE root *sed- (1) "to sit" (see sedentary).
polyhistor (n.) Look up polyhistor at Dictionary.com
"very learned person," 1580s, from Greek polyhistor "very learned," from poly "much, many" (see poly-) + histor "knowing, learned" (see history).
polymath (n.) Look up polymath at Dictionary.com
1620s, from Greek polymathes "having learned much, knowing much," from polys "much" (see poly-) + root of manthanein "to learn" (see mathematic).
polymer (n.) Look up polymer at Dictionary.com
a substance built from a large number of simple molecules of the same kind, 1855, probably from German Polymere (Berzelius, 1830), from Greek polymeres "having many parts," from polys "many" (see poly-) + meros "part" (see merit (n.)).
polymerase (n.) Look up polymerase at Dictionary.com
1866, coined by Berzelius (1830) from Greek polymeres "having many parts" (see polymer).
polymeric (adj.) Look up polymeric at Dictionary.com
1829, from polymer + -ic.
polymerization (n.) Look up polymerization at Dictionary.com
1866, from polymer + -ization.
polymerize (v.) Look up polymerize at Dictionary.com
1851, from polymer + -ize. Related: Polymerized; polymerizing.
polymorph (n.) Look up polymorph at Dictionary.com
"organism of several forms," 1828, from Greek polymorphos "of many forms" (see polymorphous).
polymorphism (n.) Look up polymorphism at Dictionary.com
1839, from polymorph + -ism.
polymorphous (adj.) Look up polymorphous at Dictionary.com
1785, from Greek polymorphos "multiform, of many forms, manifold," from poly- "many" (see poly-) + morphe "shape, form" (see Morpheus). Related: Polymorphic; polymorphously; polymorphousness.
Polynesia (n.) Look up Polynesia at Dictionary.com
1758, Latinization of French polynésie, coined 1756 by French writer Charles de Brosses (1709-1777) in "Histoire des navigations aux terres australes, contenant ce que l'on sait des moeurs et des productions des contrées découvertes jusqu'à ce jour" (and first in English in a review of it), coined from Greek polys "many" (see poly-) + nesos "island" (see Chersonese). Related: Polynesian.
polynomial Look up polynomial at Dictionary.com
1670s (n.), 1704 (adj.), irregularly formed from poly- + stem of binomial.
polyp (n.) Look up polyp at Dictionary.com
c. 1400, "nasal tumor," from Middle French polype and directly from Latin polypus "cuttlefish," also "nasal tumor," from Greek (Doric, Aeolic) polypos "octopus, cuttlefish," from polys "many" (see poly-) + pous "foot," from PIE root *ped- (1) "a foot" (see foot (n.)). Etymological sense revived 1742 as a name for hydras and sea anemones (earlier polypus, early 16c.). The Latin word is the source of French poulpe "octopus."
polypeptide (n.) Look up polypeptide at Dictionary.com
peptide built from a large number of amino acids, 1903, from German polypeptid; see poly- + peptide.
polyphagia (n.) Look up polyphagia at Dictionary.com
1690s, "eating to excess," medical Latin, from Greek polyphagia "excess in eating," from polyphagos "eating to excess," from polys "much" (see poly-) + phagein "to eat" (see -phagous). Attested from 1890 in sense "feeding on various kinds of food." Nativized as polyphagy. Related: Polyphagic; polyphagous.
Polyphemus Look up Polyphemus at Dictionary.com
name of a Cyclops ("Odyssey," IX), also used as the name for a one-eyed animal; the name is literally "many-voiced" or else "much-spoken-of" (see poly- + fame (n.)).
polyphonic (adj.) Look up polyphonic at Dictionary.com
1782, formed in English from Greek polyphonos (see polyphony).
polyphony (n.) Look up polyphony at Dictionary.com
1828, "multiplicity of sounds," from Greek polyphonia "variety of sounds," from polyphonos "having many sounds or voices," from polys "many" (see poly-) + phone "voice, sound," from PIE root *bha- (2) "to speak, tell, say" (see fame (n.)). The meaning "counterpoint" (1864) is perhaps a back-formation from the adjective.
polyploidy (n.) Look up polyploidy at Dictionary.com
1922, from German polyploidie (1910), from polyploid, from Greek poly- (see poly-) + -ploid, from comb. form of ploos "fold" (see fold (v.)) + -oid.
polyrhythm (n.) Look up polyrhythm at Dictionary.com
1911, probably a back formation from polyrhythmic.
polyrhythmic (adj.) Look up polyrhythmic at Dictionary.com
1883, from poly- + rhythmic.
polysemous (adj.) Look up polysemous at Dictionary.com
1884, from Medieval Latin polysemus, from Greek polysemos "of many sides" (see polysemy).
polysemy (n.) Look up polysemy at Dictionary.com
1900, from French polysémie (1897), from Medieval Latin polysemus, from Greek polysemos "of many senses," from poly- (see poly-) + sema "sign" (see semantic). Related: Polysemic.