a combining form meaning “fire,” “heat,” “high temperature,” used in the formation of compound words: pyrogen; pyrolusite; pyromancy.
Chemistry. a combining form used in the names of inorganic acids, indicating that the acid's water content is intermediate between that of the corresponding ortho- (more water) and meta- (least water) acids (pyroantimonic, H 4 Sb 2 O 7 , pyroarsenic, H 4 As 2 O 7 , and pyrosulfuric, H 2 S 2 O 7 , acids ). The combining form is also used in the names of the salts of these acids. If the acid ends in -ic, the corresponding salt ends in -ate (pyroboric acid, H 2 B 4 O 7 , and potassium pyrobate, K 2 B 4 O 7 , or pyrosulfuric, H 2 S 2 O 7 , and pyrosulfate, N 2 S 2 O 7 ); if the acid ends in -ous, the corresponding salt ends in -ite (pyrophosphorous acid, H 4 P 2 O 5 , potassium pyrophosphite, K 4 P 2 O 5 ).
Also, pyr-.

< Greek pyro-, combining form of pŷr fire Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
pyro- or (before a vowel) pyr-
combining form
1.  denoting fire, heat, or high temperature: pyromania; pyrometer
2.  caused or obtained by fire or heat: pyroelectricity
3.  chem
 a.  denoting a new substance obtained by heating another: pyroboric acid is obtained by heating boric acid
 b.  denoting an acid or salt with a water content intermediate between that of the ortho- and meta- compounds: pyro-phosphoric acid
4.  mineralogy
 a.  having a property that changes upon the application of heat: pyromorphite
 b.  having a flame-coloured appearance: pyroxylin
[from Gk pur fire]
pyr- or (before a vowel) pyr-
combining form
[from Gk pur fire]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

comb. form meaning "fire," from Gk. pyro-, combining form of pyr (gen. pyros) "fire" (see pyre).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

pyro- or pyr-

  1. Fire; heat: pyrophobia.

  2. Relating to the action of fire or heat: pyrolysis.

  3. Fever: pyrogen.

  4. Derived from an acid by the loss of a water molecule: pyrophosphoric acid.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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