Etymology
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*wekw- 
Proto-Indo-European root meaning "to speak."

It forms all or part of: advocate; avocation; calliope; convocation; epic; equivocal; equivocation; evoke; invoke; provoke; revoke; univocal; vocabulary; vocal; vocation; vocative; vociferate; vociferous; voice; vouch; vox; vowel.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vakti "speaks, says," vacas- "word;" Avestan vac- "speak, say;" Greek eipon (aorist) "spoke, said," epos "word;" Latin vocare "to call," vox "voice, sound, utterance, language, word;" Old Prussian wackis "cry;" German er-wähnen "to mention."
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*reudh- 
Proto-Indo-European root meaning "red, ruddy." The only color for which a definite common PIE root word has been found. The initial -e- in the Greek word is because Greek tends to avoid beginning words with -r-.

It forms all or part of: bilirubin; corroborate; Eritrea; erysipelas; erythema; erythro-; Radnor; red; redskin; roan; robust; rooibos; Rotwelsch; rouge; roux; rowan; rubella; rubicund; rubric; ruby; ruddock; ruddy; rufous; Rufus; russet; rust.

It is the hypothetical source of/evidence for its existence is provided by: Latin ruber, also dialectal rufus "light red," mostly of hair; Greek erythros; Sanskrit rudhira-; Avestan raoidita-; Old Church Slavonic rudru, Polish rumiany, Russian rumjanyj "flushed, red," of complexions, etc.; Lithuanian raudas; Old Irish ruad, Welsh rhudd, Breton ruz "red."
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*teuta- 

*teutā-, Proto-Indo-European root meaning "tribe." It forms all or part of: Deutsch; Dutch; Plattdeutsch; Teuton; Teutonic.

It is the hypothetical source of/evidence for its existence is provided by: Old Irish tuoth "people," Old Lithuanian tauta "people," Old Prussian tauto "country," Oscan touto "community," German Deutsch, Gothic þiuda, Old English þeod "people, race, nation," Old English þeodisc "belonging to the people." But Boutkan says it is probably a substratum word.

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*bhergh- (1)

Proto-Indo-European root meaning "to hide, protect." It forms all or part of: bargain; borrow; burial; bury; harbor; hauberk; scabbard.

It is the hypothetical source of/evidence for its existence is provided by: Old English Old English borgian "to lend, be surety for;" Old Church Slavonic brěgo "I preserve, guard," Lithuanian bìrginti "be parsimonious." But, absent other possible cognates, Boutkan writes that it is not certainly Indo-European and "probably a substratum word."

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*gal- 
Proto-Indo-European root meaning "to call, shout."

It forms all or part of: call; clatter; Gallic; gallinaceous; gallium; glasnost; Glagolitic.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit garhati "bewail, criticize;" Latin gallus "cock;" Old English ceallian "to shout, utter in a loud voice," Old Norse kalla "to cry loudly," Dutch kallen "to talk, chatter;" German Klage "complaint, grievance, lament, accusation;" Old English clacu "affront;" Old Church Slavonic glasu "voice," glagolu "word;" Welsh galw "call."
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*ghos-ti- 

Proto-Indo-European root meaning "stranger, guest, host," properly "someone with whom one has reciprocal duties of hospitality," representing "a mutual exchange relationship highly important to ancient Indo-European society" [Watkins]. But as strangers are potential enemies as well as guests, the word has a forked path.

The word ghos-ti- was thus the central expression of the guest-host relationship, a mutual exchange relationship highly important to ancient Indo-European society. A guest-friendship was a bond of trust between two people that was accompanied by ritualized gift-giving and created an obligation of mutual hospitality and friendship that, once established, could continue in perpetuity and be renewed years later by the same parties or their descendants. [Calvert Watkins, "American Heritage Dictionary of Indo-European Roots"]

It forms all or part of: Euxine; guest; hospice; hospitable; hospital; hospitality; hospodar; host (n.1) "person who receives guests;" host (n.2) "multitude;" hostage; hostel; hostile; hostility; hostler; hotel; Xenia; xeno-; xenon.

It is the hypothetical source of/evidence for its existence is provided by: Greek xenos "guest, host, stranger;" Latin hostis, in earlier use "a stranger," in classical use "an enemy," hospes "host;" Old Church Slavonic gosti "guest, friend," gospodi "lord, master;" Old English gæst, "chance comer, a stranger."

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*g(a)lag- 
also *g(a)lakt-, Proto-Indo-European root meaning "milk."

It forms all or part of: ablactation; cafe au lait; galactic; galaxy; lactate (v.); lactate (n.); lactation; lacteal; lactescence; lactic; lactivorous; lacto-; lactose; latte; lettuce.

It is the hypothetical source of/evidence for its existence is provided by: Latin lac (genitive lactis) "milk;" Greek gala (genitive galaktos), "milk;" Armenian dialectal kaxc' "milk." The initial "g" probably was lost in Latin by dissimilation. This and the separate root *melg-, account for words for "milk" in most of the Indo-European languages. The absence of a common word for it is considered a mystery.
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-i- 
a "connective" element in many words formed with Latin or Greek suffixes, now often felt as part of them (as in -iac, -iacal, -ial, -ian, -ify, -ity, etc.). Properly it forms no proper part of the suffix but is often the stem-vowel of the initial word in the Latin compounds (genial from genius), or a modified form of it. As such forms were very common, -i- was used merely connectively or euphonically in some Latin compounds (uniformis) and in later words made from Latin components in English or French (centennial, editorial).

The Greek equivalent is -o-, which also became an active connective in English, but they now are used indifferently with elements from either language.
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*ster- (2)

Proto-Indo-European root meaning "star." Buck and others doubt the old suggestion that it is a borrowing from Akkadian istar "venus." The source of the common Balto-Slavic word for "star" (Lithuanian žvaigždė, Old Church Slavonic zvezda, Polish gwiazda, Russian zvezda) is not explained.

It forms all or part of: aster; asterisk; asterism; asteroid; astral; astro-; astrobiology; astrobleme; astrognosy; astroid; astrolabe; astrolatry; astrology; astromancy; astronaut; astronomy; AstroTurf; constellation; disaster; Estella; Esther; instellation; interstellar; lodestar; star; stardust; starfish; starlet; starlight; starry; stellar; stellate.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit star-; Hittite shittar, Greek aster "star," with derivative astron; Latin stella, Breton sterenn, Welsh seren "star."

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*re- 

*rē-, Proto-Indo-European root meaning "to reason, count;" a variant of PIE root *ar-, also arə-, "to fit together." 

It forms all or part of: Alfred; arraign; arithmetic; Conrad; dread; Eldred; Ethelred; hatred; hundred; kindred; logarithm; Ralph; rate (n.) "estimated value or worth;" rathskeller; ratify; ratio; ration; read; reason; rede; rhyme; riddle (n.1) "word-game;" rite; ritual.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit radh- "to succeed, accomplish;" Greek arithmos "number, amount;" Latin reri "to consider, confirm, ratify," ritus "rite, religious custom;" Old Church Slavonic raditi "to take thought, attend to;" Old Irish im-radim "to deliberate, consider;" Old English rædan "to advise, counsel, persuade; read;" Old English, Old High German rim "number;" Old Irish rim "number," dorimu "I count."

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