pyrexia vs fever

pyrexia and fever both are nouns.

Word	Noun	Adjective	Verb	Adverb
pyrexia	Yes	No	No	No
fever	Yes	No	No	No

As nouns, pyrexia and fever are synonyms defined as:

pyrexia and fever: a rise in the temperature of the body; frequently a symptom of infection

Other synonyms of pyrexia include febricity, febrility, feverishness.

pyrexia (noun)	fever (noun)
a rise in the temperature of the body; frequently a symptom of infection	a state of nervous excitement
	a rise in the temperature of the body; frequently a symptom of infection