1. Thick, sticky, stringy mucus secreted by the mucous membrane of the respiratory tract, as during a cold or other respiratory infection.
2. One of the four humors of ancient and medieval physiology, thought to cause sluggishness, apathy, and evenness of temper.
3. Sluggishness of temperament.
4. Calm self-possession; equanimity.
[Middle English fleume, mucous discharge, the humor phlegm, from Old French, from Medieval Latin phlegma, flegma, from Late Latin phlegma, the humor phlegm, from Greek, heat, the humor phlegm, from phlegein, to burn.]
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.