pyrexia vs symptom

pyrexia and symptom both are nouns.

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

As nouns, symptom is a hypernym of pyrexia; that is, symptom is a word with a broader meaning than pyrexia:

pyrexia: a rise in the temperature of the body; frequently a symptom of infection
symptom: (medicine) any sensation or change in bodily function that is experienced by a patient and is associated with a particular disease

pyrexia (noun)	symptom (noun)
a rise in the temperature of the body; frequently a symptom of infection	anything that accompanies X and is regarded as an indication of X's existence
	(medicine) any sensation or change in bodily function that is experienced by a patient and is associated with a particular disease