a rise in the temperature of the body; frequently a symptom of infection
"After catching the flu, she developed a high fever that made her feel extremely hot and weak."
A higher than normal body temperature of a person (or, generally, a mammal), usually caused by disease.
"The doctor examined the child to determine if her fever was caused by an infection or just warm weather."
In plain English: Fever is when your body temperature gets higher than normal because you are sick.
"The doctor said she had to rest at home because her fever was too high."
Usage: Use the noun fever to describe an abnormally high body temperature typically resulting from illness or infection. While it can function as a verb meaning to induce such heat, this usage is rare and usually appears in literary contexts rather than everyday speech.
To put into a fever; to affect with fever.
"The hot spring was said to have the power to fever any patient suffering from a lingering chill."
In plain English: To fever is to become extremely excited and anxious about something, usually because you are waiting for news that might be bad.
"The crowd began to fever with excitement before the concert started."
The word fever entered Middle English from the Latin febris, which originally meant "a burning." This term eventually replaced an older native Old English word for the same condition.