pyrexia (n.)

"fever, a higher bodily temperature than is normal," 1769, medical Latin, from Greek pyrexis "feverishness," from pyressein "to be feverish, to be ill of fever," from pyretos "fever, burning heat" (related to pyr "fire," from PIE root *paewr- "fire") + abstract noun ending -ia. Formerly sometimes nativized as pyrexy. Related: Pyrexial; pyrexic; pyrexical.