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.
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."
"pile or heap of wood or other combustible materials for burning a dead body," 1650s, from Latin pyra and directly from Greek pyra (Ionic pyrē) "funeral pyre; altar for sacrifice; watch-fire; hearth; any place where fire is kindled," from pyr "fire" (from PIE root *paewr- "fire," source also of fire (n.)). Related: Pyral.