The Collaborative International Dictionary
Pyr-
Pyro- \Pyro-\, Pyr- \Pyr-\ . [Gr. ?, ?, fire.] Combining forms designating fire or heat; specifically (Chem.), used to imply an actual or theoretical derivative by the action of heat; as in pyrophosphoric, pyrosulphuric, pyrotartaric, pyrotungstic, etc.
Wiktionary
pyr-
pre. (alternative form of pyro- English)