Is it farther or further?
before vowels pyr-, word-forming element form meaning "fire," from Greek pyro-, combining form of pyr (genitive pyros) "fire, funeral fire," also symbolic of terrible things, rages, "rarely as an image of warmth and comfort" [Liddell & Scott]; see fire (n.). Pyriphlegethon, literally "fire-blazing," was one of the rivers of Hell.
pyro- or pyr-
Fire; heat: pyrophobia.
Relating to the action of fire or heat: pyrolysis.
Derived from an acid by the loss of a water molecule: pyrophosphoric acid.