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[pahy-roh] /ˈpaɪ roʊ/
noun, plural pyros. Informal.
a pyromaniac.
Origin of pyro
by shortening; cf. -o


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. 2018.
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British Dictionary definitions for pyro


combining form
denoting fire, heat, or high temperature: pyromania, pyrometer
caused or obtained by fire or heat: pyroelectricity
  1. denoting a new substance obtained by heating another: pyroboric acid is obtained by heating boric acid
  2. denoting an acid or salt with a water content intermediate between that of the ortho- and meta- compounds: pyro-phosphoric acid
  1. having a property that changes upon the application of heat: pyromorphite
  2. having a flame-coloured appearance: pyroxylin
Word Origin
from Gk pur fire
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for pyro


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.

Online Etymology Dictionary, © 2010 Douglas Harper
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pyro in Medicine

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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Slang definitions & phrases for pyro



A pyromaniac, lover of fire (1977+)

The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D.
Copyright (C) 2007 by HarperCollins Publishers.
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