What does fever mean?
Fever refers primarily to an abnormal elevation of body temperature, most often triggered by infection, when the immune system deliberately raises the body's thermostat to fight off pathogens. In everyday use it describes this physiological state — as in a high fever, hay fever, or scarlet fever — and it also carries a vivid figurative meaning: a state of intense, often contagious excitement or unrest, as in election fever or gold fever. The word's connotations differ sharply between these senses; medically it signals illness and concern, while figuratively it suggests energy that can be thrilling but also volatile and potentially irrational. Derived forms such as feverish and fevered extend both senses into adjectival use, describing flushed, restless bodies or frantic activity. Few words move so naturally between the clinic and the crowd, which makes fever both practically essential and rhetorically powerful in English.
An abnormally high body temperature, typically a symptom of infection or illness.
"He developed a fever two days after the surgery."
Medically defined as a core temperature above roughly 38°C (100.4°F); clinicians call it pyrexia.
A state of intense excitement, nervous energy, or widespread enthusiasm.
"Cabin fever set in after a week trapped indoors by the storm."
Usually uncountable when referring to the condition generally; the plural is common when naming specific diseases (e.g. yellow fevers) or repeated episodes.
"The clinic treated hundreds of children suffering from recurring fevers."
Before the 20th century, fever was one of humanity's deadliest adversaries — and raising body temperature is actually your immune system's deliberate weapon against infection.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of fever
Fever comes from Old English 'fefer', borrowed from Latin 'febris', meaning fever. Latin febris is of uncertain ultimate origin, though it may relate to a root meaning 'to burn' or 'to smoke'. The same Latin root gave English the adjective 'febrile' and the verb 'defervesce', describing the subsiding of a fever. The word has been part of English since its earliest recorded stages, carried over from Germanic adoption of the Latin term.
Related word forms
How fever is actually used
In medical contexts, 'pyrexia' is the formal clinical term for fever. The figurative sense often appears in phrases like 'a fever of anticipation' and frequently carries connotations of collective emotion that can turn irrational, as in 'war fever' or 'gold fever.'
Easily confused with fever
Fever is the noun denoting elevated body temperature or intense excitement; feverish is an adjective describing someone suffering from a fever or something marked by frenzied activity.