phlo·gis·ton (flō-jĭstŏn′, -tən)
A hypothetical substance formerly thought to be a volatile constituent of all combustible substances, released as flame in combustion.
[From Greek, neuter of phlogistos, inflammable, from phlogizein, to set on fire, from phlox, phlog-, flame; see bhel-1 in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.