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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.]