Etymology
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*paewr- 
*paəwr-, Proto-Indo-European root meaning "fire."

It forms all or part of: antipyretic; burro; empyreal; empyrean; fire; pyracanth; pyre; pyretic; pyrexia; pyrite; pyro-; pyrolusite; pyromania; pyrrhic; sbirro.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit pu, Hittite pahhur "fire;" Armenian hur "fire, torch;" Czech pyr "hot ashes;" Greek pyr, Umbrian pir "fire;" Old English fyr, German Feuer "fire."
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*ater- 
*āter-, Proto-Indo-European root meaning "fire." It forms all or part of: atrabiliary; atrabilious; atrium; atrocious.

It is the hypothetical source of/evidence for its existence is provided by: Old Persian atar "fire;" Latin ater "black" ("blackened by fire"), atrox "frightful" ("of fiery or threatening appearance").
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*ker- (3)

Proto-Indo-European root meaning "heat, fire."

It forms all or part of: carbon; carboniferous; carbuncle; cremate; cremation; hearth.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit kudayati "singes;" Latin carbo "a coal, glowing coal; charcoal," cremare "to burn;" Lithuanian kuriu, kurti "to heat," karštas "hot," krosnis "oven;" Old Church Slavonic kurjo "to smoke," krada "fireplace, hearth;" Russian ceren "brazier;" Old High German harsta "roasting;" Gothic hauri "coal;" Old Norse hyrr "fire;" Old English heorð "hearth."

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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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*bhel- (1)

Proto-Indo-European root meaning "to shine, flash, burn," also "shining white" and forming words for bright colors.

It forms all or part of: beluga; Beltane; black; blancmange; blanch; blank; blanket; blaze (n.1) "bright flame, fire;" bleach; bleak; blemish; blench; blende; blend; blind; blindfold; blitzkrieg; blond; blue (adj.1); blush; conflagration; deflagration; effulgence; effulgent; flagrant; flambe; flambeau; flamboyant; flame; flamingo; flammable; Flavian; Flavius; fulgent; fulminate; inflame; inflammable; phlegm; phlegmatic; phlogiston; phlox; purblind; refulgent; riboflavin.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit bhrajate "shines;" Greek phlegein "to burn;" Latin flamma "flame," fulmen "lightning," fulgere "to shine, flash," flagrare "to burn, blaze, glow;" Old Church Slavonic belu "white;" Lithuanian balnas "pale."

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*bhreu- 
also *bhreuə-, *bhreəu-, Proto-Indo-European root meaning "to boil, bubble, effervesce, burn," with derivatives referring to cooking and brewing.

It forms all or part of: barm; barmy; bourn (n.1) "small stream;" braise; bratwurst; brawn; brawny; braze (v.1) "to expose to the action of fire;" brazier; Brazil; bread; breed; brew; broth; broil (v.2) "to quarrel, brawl;" brood; effervesce; effervescence; effervescent; embroil; ferment; fervent; fervid; fervor; imbroglio.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit bhurnih "violent, passionate;" Greek phrear "well, spring, cistern;" Latin fervere "to boil, foam," Thracian Greek brytos "fermented liquor made from barley;" Russian bruja "current;" Old Irish bruth "heat;" Old English breowan "to brew," beorma "yeast;" Old High German brato "roast meat."
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