Online Etymology Dictionary

polonium (n.): 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.): 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.): "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-: 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 (source also of 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.): by 1972, from poly- + amorous. Related: Polyamory.
polyandria (n.): 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.): 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.): 1767, nativized form of polyandria. Related: Polyandrist.
polycentric (adj.): 1826, from poly- + centric.
polychrome (adj.): "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.): "place for treatment of various diseases," 1890, from poly- "many" + clinic.
polydactyl (n.): 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.): "excessive thirst," 1650s, from Greek polydipsios "very thirsty," from poly- (see poly-) + dipsa "thirst" + -ia "condition of."
Polydorus: 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.): 1929, formed from polymer + ester. Polyester fiber was discovered 1941.
polyethylene (n.): polymer of ethylene, 1862, from French polyéthylène; see poly- + ethylene. Related: Polyethylenic (1860).
polygamous (adj.): 1610s, from polygamy + -ous, or else from Late Greek polygamos "often married." Related: Polygamously.
polygamy (n.): 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.): "plurality of origins," 1858, from poly- + -genesis "birth, origin, creation." Related: Polygenetic (1851).
polygenic (adj.): 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.): "composed of many kinds," 1797; see poly- + genus.
polyglot (adj.): 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.): 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.): 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.): 1780, "condition of having many wives," from poly- "many" (see poly-) + Greek gyne "woman, wife" (see queen). Related: Polygynous.
polyhedral (adj.): 1741, from polyhedron + -al (1).
polyhedron (n.): 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.): "very learned person," 1580s, from Greek polyhistor "very learned," from poly "much, many" (see poly-) + histor "knowing, learned" (see history).
polymath (n.): 1620s, from Greek polymathes "having learned much, knowing much," from polys "much" (see poly-) + root of manthanein "to learn" (see mathematic).
polymer (n.): 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.): 1866, coined by Berzelius (1830) from Greek polymeres "having many parts" (see polymer).
polymeric (adj.): 1829, from polymer + -ic.
polymerization (n.): 1866, from polymer + -ization.
polymerize (v.): 1851, from polymer + -ize. Related: Polymerized; polymerizing.
polymorph (n.): "organism of several forms," 1828, from Greek polymorphos "of many forms" (see polymorphous).
polymorphism (n.): 1839, from polymorph + -ism.
polymorphous (adj.): 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.): 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: 1670s (n.), 1704 (adj.), irregularly formed from poly- + stem of binomial.
polyp (n.): 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.): peptide built from a large number of amino acids, 1903, from German polypeptid; see poly- + peptide.
polyphagia (n.): 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: 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.): 1782, formed in English from Greek polyphonos (see polyphony).
polyphony (n.): 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.): 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.): 1911, probably a back formation from polyrhythmic.
polyrhythmic (adj.): 1883, from poly- + rhythmic.
polysemous (adj.): 1884, from Medieval Latin polysemus, from Greek polysemos "of many sides" (see polysemy).
polysemy (n.): 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.