Etymology
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*upo 

Proto-Indo-European root meaning "under," also "up from under," hence "over."

It forms all or part of: above; assume; Aufklarung; eave; eavesdropper; hyphen; hypo-; hypochondria; hypocrisy; hypotenuse; hypothalamus; hypothesis; hypsi-; hypso-; opal; open; oft; often; resuscitate; somber; souffle; source; soutane; souvenir; sub-; subject; sublime; subpoena; substance; subterfuge; subtle; suburb; succeed; succinct; succor; succubus; succumb; sudden; suffer; sufficient; suffix; suffrage; suggestion; summon; supine; supple; supply; support; suppose; surge; suspect; suspend; sustain; up; up-; Upanishad; uproar; valet; varlet; vassal.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit upa "near, under, up to, on," Greek hypo "under," Latin sub "under, below," Gothic iup, Old Norse, Old English upp "up, upward," Hittite up-zi "rises."

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*as- 

also *es-, Proto-Indo-European root meaning "to burn, glow." 

It forms all or part of: ardent; ardor; area; arid; aridity; aril; arson; ash (n.1) "powdery remains of fire;" azalea; potash; potassium.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit asah "ashes, dust;" Hittite hat- "to dry up;" Greek azein "to dry up, parch," azaleos "dry;" Latin aridus "parched, dry," ārēre "to be dry," āra "altar, hearth;" Armenian azazem "I dry up;" Old English æsce "ash," Old High German asca, Gothic azgo "ashes." 

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*ters- 
Proto-Indo-European root meaning "to dry."

It forms all or part of: inter; Mediterranean; metatarsal; parterre; subterranean; tarsal; tarsus; Tartuffe; terra; terrace; terra-cotta; terrain; terran; terraqueous; terrarium; terrene; terrestrial; terrier; territory; thirst; toast; torrent; torrid; turmeric; tureen.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit tarsayati "dries up;" Avestan tarshu- "dry, solid;" Greek teresesthai "to become or be dry," tersainein "to make dry;" Latin torrere "dry up, parch," terra "earth, land;" Gothic þaursus "dry, barren," Old High German thurri, German dürr, Old English þyrre "dry;" Old English þurstig "thirsty."
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*al- (2)
Proto-Indo-European root meaning "to grow, nourish."

It forms all or part of: abolish; adolescent; adult; alderman; aliment; alimony; Alma; alma mater; alt (2) "high tone;" alti-; altimeter; altitude; alto; alumnus; auld; coalesce; elder (adj., n.1); eldest; Eldred; enhance; exalt; haught; haughty; hautboy; hawser; oboe; old; proletarian; proliferation; prolific; world.

It is the hypothetical source of/evidence for its existence is provided by: Greek aldaino "make grow, strengthen," althein, althainein "to get well;" Latin alere "to feed, nourish, suckle; bring up, increase," altus "high," literally "grown tall," almus "nurturing, nourishing," alumnus "fosterling, step-child;" Gothic alþeis, Dutch oud, German alt "old;" Gothic alan "to grow up," Old Norse ala "to nourish;" Old Irish alim "I nourish."
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*pel- (2)

Proto-Indo-European root meaning "to fold."

It forms all or part of: aneuploidy; decuple; fold (v.); -fold; furbelow; haplo-; hundredfold; manifold; multiple; octuple; polyploidy; -plus; quadruple; quintuple; sextuple; triple.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit putah "fold, pocket;" Albanian pale "fold;" Middle Irish alt "a joint;" Lithuanian pelti "to plait;" Old English faldan "to fold, wrap up, furl."

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*pleu- 
Proto-Indo-European root meaning "to flow."

It forms all or part of: fletcher; fledge; flee; fleet (adj.) "swift;" fleet (n.2) "group of ships under one command;" fleet (v.) "to float, drift; flow, run;" fleeting; flight (n.1) "act of flying;" flight (n.2) "act of fleeing;" flit; float; flood; flotsam; flotilla; flow; flue; flugelhorn; fluster; flutter; fly (v.1) "move through the air with wings;" fly (n.) "winged insect;" fowl; plover; Pluto; plutocracy; pluvial; pneumo-; pneumonia; pneumonic; pulmonary.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit plavate "navigates, swims;" Greek plynein "to wash," plein "to navigate," ploein "to float, swim," plotos "floating, navigable," pyelos "trough, basin;" Latin plovere "to rain," pluvius "rainy;" 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."
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*stel- 

Proto-Indo-European root meaning "to put, stand, put in order," with derivatives referring to a standing object or place.

It forms all or part of: apostle; catastaltic; diastole; epistle; forestall; Gestalt; install; installment; pedestal; peristalsis; peristaltic; stale (adj.); stalk (n.); stall (n.1) "place in a stable for animals;" stall (n.2) "pretense to avoid doing something;" stall (v.1) "come to a stop, become stuck;" stallage; stallion; stele; stell; still (adj.); stilt; stole (n.); stolid; stolon; stout; stultify; systaltic; systole.

It is the hypothetical source of/evidence for its existence is provided by: Greek stellein "to put in order, make ready; equip or dress with weapons, clothes, etc.; prepare (for a journey), dispatch; to furl (sails);" Armenian stełc-anem "to prepare, create;" Albanian shtiell "to wind up, reel up, collect;" Old Church Slavonic po-steljo "I spread;" Old Prussian stallit "to stand;" Old English steall "standing place, stable," Old High German stellen "to set, place."

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*eu- 
Proto-Indo-European root meaning "to dress," with extended form *wes- (2) "to clothe."

It forms all or part of: divest; exuviae; invest; revetment; transvestite; travesty; vest; vestry; wear.

It is the hypothetical source of/evidence for its existence is provided by: Hittite washshush "garments," washanzi "they dress;" Sanskrit vaste "he puts on," vasanam "garment;" Avestan vah-; Greek esthes "clothing," hennymi "to clothe," eima "garment;" Latin vestire "to clothe;" Welsh gwisgo, Breton gwiska; Old English werian "to clothe, put on, cover up," wæstling "sheet, blanket."
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*wer- (1)

Proto-Indo-European root meaning "to raise, lift, hold suspended." 

It forms all or part of: aerate; aeration; aerial; aero-; aerobics; aerophyte; aerosol; air (n.1) "invisible gases that surround the earth;" airy; aorta; anaerobic; aria; arterial; arterio-; arteriosclerosis; arteriole; artery; aura; malaria; meteor

It is the hypothetical source of/evidence for its existence is provided by: Greek aerein "to lift, raise up;" Lithuanian svarus "heavy," sverti "to lift, weigh;" Old English swar, Old Norse svarr, Old High German swar, German schwer "heavy."

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*keue- 
*keuə-, Proto-Indo-European root meaning "to swell," also "vault, hole."

It forms all or part of: accumulate; accumulation; cave; cavern; cavity; coeliac; church; codeine; coelacanth; coeliac; coelomate; concave; cumulate; cumulative; cumulus; enceinte; excavate; kirk; kymatology; Kyrie eleison.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit svayati "swells up, is strong;" Greek kyein "to swell," koilos "hollow, hollowed out, spacious, deep;" Latin cumulus "a heap, pile, mass, surplus;" Lithuanian šaunas "firm, solid, fit, capable;" Middle Irish cua "hollow;" Armenian soyl "cavity."
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