Etymology
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warmth (n.)
late 12c., wearmth, Proto-Germanic *warmitho- (source also of Middle Low German wermede, Dutch warmte), from *warmo- (see warm (adj.); also see -th (2)).
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coolth (n.)

1540s, from cool on the model of warmth. It persists, and was used by Pound, Kipling, etc., but it never has shaken its odor of facetiousness and become standard.

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beek (v.)
"to bask in the warmth" of something, early 13c., a northern and Scottish word of unknown origin; perhaps ultimately connected to bake (v.).
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ardency (n.)
1540s, "warmth of feeling, desire," from ardent + -cy. A figurative sense, the literal meaning "intensity of heat" is attested from 1630s.
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enthalpy (n.)
1927 in physics, from Greek enthalpein "to warm in," from en "in" (see en- (2)) + thalpein "to heat," from thalpos "warmth, heat," especially "summer heat."
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cool (v.)

Old English colian, "to lose warmth," also figuratively, "to lose ardor;" cognate with Old Saxon kolon, Dutch koelen, Old High German chuolan, German kühlen, all from the root of cool (adj.). Transitive meaning "to cause to lose warmth, reduce the temperature of" is from late 14c. Related: Cooled; cooling.  

Figurative meaning "abate the intensity of" is from c. 1300. To cool (one's) heels" wait in attendance, "generally applied to detention at a great man's door" [Century Dictionary] is attested from 1630s; probably the notion is "to rest one's feet after walking."

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campfire (n.)

also camp-fire, "fire in a camp for warmth or cooking," 1835, from camp (n.) + fire (n.). In the GAR (Civil War Northern veterans' society), "a meeting or reunion of members of a post" (1874).

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fervor (n.)
mid-14c., "warmth or glow of feeling," from Old French fervor "heat; enthusiasm, ardor, passion" (12c., Modern French ferveur), from Latin fervor "a boiling, violent heat; passion, ardor, fury," from fervere "to boil; be hot" (from PIE root *bhreu- "to boil, bubble, effervesce, burn").
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pyro- 

before vowels pyr-, word-forming element form meaning "fire," from Greek pyr (genitive pyros) "fire, funeral fire," also symbolic of terrible things, rages, "rarely as an image of warmth and comfort" [Liddell & Scott], from PIE root *paewr- "fire." Pyriphlegethon, literally "fire-blazing," was one of the rivers of Hell.

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lukewarm (adj.)

"neither cold nor hot, tepid," late 14c., from warm (adj.) + luke (adj.) "tepid" (c. 1200), a word of unknown origin. 

Figurative sense of "lacking in zeal, not ardent" (of persons or their actions) is from 1520s. Related: Lukewarmly; lukewarmness. Luke-warmth (1590s) is marked "rare" in OED.

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