1. Combining form denoting fire, heat, or fever.
2. In chemistry, combining form denoting derivatives formed by removal of water (usually by heat) to form anhydrides.
The definition information for pyro- is provided by Stedman's. You can search our medical dictionary here.
Stedman's, part of Lippincott Williams & Wilkins, provides a comprehensive line of health-science publications for healthcare professionals and medical students.