What does coma mean?
A coma is a prolonged state of deep unconsciousness in which a person sleeps and cannot be woken, showing little or no response to sound, touch, or pain. It results when injury, disease, drugs, or metabolic disruption impair the brain's arousal systems, and it ranges in depth from light unresponsiveness to profound insensibility. Medically, a coma is distinct from sleep because it cannot be interrupted by external stimulation, and patients may require intensive support until they recover, transition to other states of impaired consciousness, or do not survive. The word carries serious, somber connotations and appears constantly in news reporting on accidents and illness. Beyond medicine, astronomers use 'coma' to name the hazy cloud of gas and dust that surrounds a comet's nucleus as it nears the sun — a separate sense borrowed from a different Greek root meaning hair. Related terms include 'comatose', describing someone in or like such a state.
A prolonged state of deep unconsciousness from which a person cannot be aroused by ordinary stimuli.
"She spent two months in a coma following the stroke."
Almost always what people mean by the word in general conversation.
The diffuse cloud of gas and dust surrounding the nucleus of an active comet.
"As the comet approached perihelion, its coma brightened dramatically."
Pluralized as 'comae' in technical astronomy literature.
An optical aberration causing off-axis points of light to appear as comet-shaped blurs instead of sharp points.
"The telescope showed noticeable coma at the edges of the field."
Strictly a technical term in optics.
The everyday medical sense takes the regular plural 'comas'. In astronomy and optics, the learned plural 'comae' (pronounced KOH-mee) is standard in technical literature.
"The hospital treated several patients in diabetic comas that winter."
Astronomers borrowed 'coma' twice from the Greeks — once for a sleeper who cannot wake, and once for the hazy halo of light around a comet's heart, which comes from an entirely different Greek word meaning 'hair'.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of coma
The medical sense of 'coma' entered English in the mid-17th century from Latin, which took it from Greek kōma, meaning deep sleep or stupor — a term ancient Greek physicians already applied to states of pathological unresponsiveness. The astronomical sense has a different source: it derives from Greek komē, meaning 'hair', the root behind 'comet' (literally 'long-haired star'), and was adopted into scientific Latin for the fuzzy envelope around a comet's head. Thus one English word preserves two distinct classical roots, both describing things that appear dormant or diffuse.
Related word forms
How coma is actually used
In everyday usage 'coma' almost always refers to the medical condition, so the plural form 'comae' belongs almost entirely to scientific writing about comets. The adjective 'comatose' describes someone in or resembling such a state and is also used figuratively for sluggishness or unresponsiveness.
Easily confused with coma
A comma is the punctuation mark (,) used to separate parts of a sentence, while a coma is a state of prolonged unconsciousness.