HYPERPYREXIA
hyperpyrexia
(noun) extremely high fever (especially in children)
Source: WordNet® 3.1
Etymology
Noun
hyperpyrexia (countable and uncountable, plural hyperpyrexias)
(medicine) An excessive and unusual elevation of set body temperature greater than or equal to 41°C (105.8°F), or extremely high fever.
Source: Wiktionary
Hy`per*py*rex"i*a, n. Etym: [NL. See Hyper-, and Pyrexia.] (Med.)
Definition: A condition of excessive fever; an elevation of temperature in
a disease, in excess of the limit usually observed in that disease.
Source: Webster’s Unabridged Dictionary 1913 Edition