Etymology
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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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igneo- 
word-forming element meaning "of fire; of fire and; of igneous origin," from Latin igneus (see igneous).
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