pyro

US: (pī′rō)

WordReference Random House Unabridged Dictionary of American English © 2025

py•ro  (pī′rō), n., pl. -ros. [Informal.]

1. Informal Terms a pyromaniac.

• compare -o by shortening

pyro-, 

1. a combining form meaning "fire,'' "heat,'' "high temperature,'' used in the formation of compound words:
   pyrogen;
   pyrolusite;
   pyromancy.
2. 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, H₄Sb₂O₇, pyroarsenic, H₄As₂O₇, and pyrosulfuric, H₂S₂O₇, 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, H₂B₄O₇, and potassium pyrobate, K₂B₄O₇, or pyrosulfuric, H₂S₂O₇, and pyrosulfate, N₂S₂O₇);
   if the acid ends in -ous, the corresponding salt ends in -ite (pyrophosphorous acid, H₄P₂O₅, potassium pyrophosphite, K₄P₂O₅).
Also, pyr-. 
• Greek pyro-, combining form of pŷr fire

WordReference Random House Learner's Dictionary of American English © 2025

pyro-, prefix. 

1. pyro- comes from Greek, where it has the meaning "fire, heat, high temperature'':
   pyromania, pyrotechnics.

Collins Concise English Dictionary © HarperCollins Publishers::

pyro-, (before a vowel)pyr- combining_form

1. denoting fire, heat, or high temperature: pyromania, pyrometer
2. denoting a new substance obtained by heating another: pyroboric acid is obtained by heating boric acid
3. having a property that changes upon the application of heat
4. having a flame-coloured appearance: pyroxylin

Etymology: from Gk pur fire