From The Collaborative International Dictionary of English v.0.48:
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.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48:
Pyro \Py"ro\, n. (Photog.)
Abbreviation of pyrogallic acid. [Colloq.]
[1913 Webster]