hyperpyrexia vs febrility

hyperpyrexia and febrility both are nouns.

Word	Noun	Adjective	Verb	Adverb
hyperpyrexia	Yes	No	No	No
febrility	Yes	No	No	No

As nouns, febrility is a hypernym of hyperpyrexia; that is, febrility is a word with a broader meaning than hyperpyrexia:

hyperpyrexia: extremely high fever (especially in children)
febrility: a rise in the temperature of the body; frequently a symptom of infection

Other hypernyms of hyperpyrexia include hyperthermia, hyperthermy, febricity, fever, feverishness, pyrexia.

hyperpyrexia (noun)	febrility (noun)
extremely high fever (especially in children)	a rise in the temperature of the body; frequently a symptom of infection