What does phlegm mean?
Phlegm is a noun with two main uses. In its everyday medical sense, it means thick mucus produced by the throat and respiratory tract, particularly during a cough, cold, or chest infection. The word can describe either the material itself or a congested condition, as in “chest full of phlegm.” In older and literary English, phlegm also refers to a supposedly calm, sluggish, or unfeeling temperament. This figurative use survives most clearly in “phlegmatic,” an adjective meaning slow-moving, unemotional, or difficult to rouse. The word reflects an ancient medical theory that the body's humours influenced both physical health and personality. Today, the medical sense is dominant, while the character-based sense generally sounds old-fashioned or disapproving.
Thick mucus produced by the respiratory tract, especially during a cough, cold, or chest infection.
"Her cough brought up a large amount of phlegm."
Common in medical and everyday health contexts. It is usually an uncountable mass noun, though “phlegms” is occasionally used when referring to separate portions or acts of expectoration.
A calm, sluggish, or supposedly unfeeling temperament.
"His phlegm in the face of danger seemed to his colleagues like indifference."
This sense is archaic or literary and is now more commonly encountered through the derivative “phlegmatic”; when used of a person, it may be mildly disparaging.
Usually uncountable when referring to mucus as a substance. The plural is uncommon but can be used for separate portions of phlegm.
"The doctor asked whether the patient was bringing up phlegms during the night."
Phlegm was once tied to the ancient belief that one of the body's four humours determined a person's temperament, giving us the phrase 'phlegmatic' for someone slow to react.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does phlegm come from?
The word comes through Latin from Greek phlegma, a term associated with mucus and also used in ancient medical theory for one of the bodily humours. In English, the medical sense developed from the ordinary meaning of mucus, while the figurative sense reflects the older association of phlegmatic temperament with an excess of the supposed phlegmatic humour. Related words include phlegmatic, phlegmatically, and the medical term phlegmon.
Related word forms
How phlegm is actually used
In medical contexts, phlegm generally refers to mucus from the respiratory tract and is distinct from sputum, which more specifically includes material coughed up from the lungs and lower airways. The figurative sense is now mostly literary, historical, or mildly disparaging.
Easily confused with phlegm
Phlegm is mucus produced by the respiratory tract, whereas phlegmon is a medical term for an infection or inflammation of connective tissue.