Etymology
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*ghredh- 

Proto-Indo-European root meaning "to walk, go." 

It forms all or part of: aggress; aggression; aggressive; centigrade; congress; degrade; degree; degression; digress; digression; egress; gradation; grade; gradual; graduate; grallatorial; gravigrade; ingredient; ingress; plantigrade; progress; progression; regress; regression; retrograde; retrogress; tardigrade; transgress; transgression.

It is the hypothetical source of/evidence for its existence is provided by: Latin gradus "a step, a pace, gait," figuratively "a step toward something, a degree of something rising by stages;" gradi "to walk, step, go;" Lithuanian gridiju, gridyti "to go, wander;" Old Church Slavonic gredo "to come;" Old Irish in-greinn "he pursues."  

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*we- 

wē-, Proto-Indo-European root meaning "to blow." 

It forms all or part of: Nirvana; vent; ventilate; weather; wind (n.1) "air in motion;" window; wing.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit va-, Greek aemi-, Gothic waian, Old English wawan, Old High German wajan, German wehen, Old Church Slavonic vejati "to blow;" Sanskrit vatah, Avestan vata-, Hittite huwantis, Latin ventus, Old English wind, German Wind, Gothic winds, Old Church Slavonic vetru, Lithuanian vėjas "wind;" Lithuanian vėtra "tempest, storm;" Old Irish feth "air;" Welsh gwynt, Breton gwent "wind." 

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*bhle- 
bhlē-, Proto-Indo-European root meaning "to blow," possibly a variant of PIE root *bhel- (2) "to blow, swell."

It forms all or part of: afflatus; bladder; blase; blast; blather; blaze (v.2) "make public;" blow (v.1) "move air;" conflate; deflate; flageolet; flatulent; flatus; flavor; inflate; inflation; insufflation; isinglass; souffle.
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*merg- 
Proto-Indo-European root meaning "boundary, border."

It forms all or part of: Cymric; demarcation; Denmark; emarginate; landmark; march (v.) "walk with regular tread;" march (n.2) "boundary;" marchioness; margin; margrave; mark (n.1) "trace, impression;" mark (n.2) "unit of money or weight;" marque; marquee; marquetry; marquis; remark; remarkable.

It is the hypothetical source of/evidence for its existence is provided by: Latin margo "margin;" Avestan mareza- "border;" Old Irish mruig, Irish bruig "borderland," Welsh bro "district;" Old English mearc "boundary, sign, limit, mark," Gothic marka "boundary, frontier."
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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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*gwa- 

*gwā-, also *gwem-, Proto-Indo-European root meaning "to go, come."

It forms all or part of: acrobat; adiabatic; advent; adventitious; adventure; amphisbaena; anabasis; avenue; base (n.) "bottom of anything;" basis; become; circumvent; come; contravene; convene; convenient; convent; conventicle; convention; coven; covenant; diabetes; ecbatic; event; eventual; hyperbaton; hypnobate; intervene; intervenient; intervention; invent; invention; inventory; juggernaut; katabatic; misadventure; parvenu; prevenient; prevent; provenance; provenience; revenant; revenue; souvenir; subvention; supervene; venire; venue; welcome.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit gamati "he goes," Avestan jamaiti "goes," Tocharian kakmu "come," Lithuanian gemu, gimti "to be born," Greek bainein "to go, walk, step," Latin venire "to come," Old English cuman "come, approach," German kommen, Gothic qiman.

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*deks- 

Proto-Indo-European root meaning "right, opposite left," hence "south" (from the viewpoint of one facing east).

It forms all or part of: ambidexterity; ambidextrous; deasil; destrier; Dexter; dexterity; dexterous; dextro-.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit daksinah "on the right hand, southern, skillful;" Avestan dashina- "on the right hand;" Greek dexios "on the right hand," also "fortunate, clever;" Latin dexter "skillful," also "right (hand);" Old Irish dess "on the right hand, southern;" Welsh deheu; Gaulish Dexsiva, name of a goddess of fortune; Gothic taihswa; Lithuanian dešinas; Old Church Slavonic desnu, Russian desnoj

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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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*wel- (3)
Proto-Indo-European root meaning "to turn, revolve," with derivatives referring to curved, enclosing objects.

It forms all or part of: archivolt; circumvolve; convoluted; convolution; devolve; elytra; evolution; evolve; Helicon; helicopter; helix; helminth; lorimer; ileus; involve; revolt; revolution; revolve; valve; vault (v.1) "jump or leap over;" vault (n.1) "arched roof or ceiling;" volte-face; voluble; volume; voluminous; volute; volvox; volvulus; vulva; wale; walk; wallet; wallow; waltz; well (v.) "to spring, rise, gush;" welter; whelk; willow.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit valate "turns round," ulvam "womb, vulva;" Lithuanian valtis "twine, net," vilnis "wave," apvalus "round;" Old Church Slavonic valiti "roll, welter," vlŭna "wave;" Greek eluein "to roll round, wind, enwrap," eilein "twist, turn, squeeze; revolve, rotate," helix "spiral object;" Latin volvere "to turn, twist;" Gothic walwjan "to roll;" Old English wealwian "roll," weoloc "whelk, spiral-shelled mollusk;" Old High German walzan "to roll, waltz;" Old Irish fulumain "rolling;" Welsh olwyn "wheel."
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*ko- 

Proto-Indo-European root, the stem of demonstrative pronoun meaning "this."

It forms all or part of: cis-; et cetera; harass; he; hence; her; here; him; his; hither; it.

It is the hypothetical source of/evidence for its existence is provided by:  Greek ekeinos "that person;" Latin cis "on this side," citra (adv.) "on this side;" Old Church Slavonic si, Lithuanian is, Hittite ki "this;" Old English hider, Gothic hidre "hither."

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