earlier also feaver, late Old English fefor, fefer "fever, temperature of the body higher than normal," from Latin febris "fever," related to fovere "to warm, heat," which is probably from PIE root *dhegh- "burn" (source also of Gothic dags, Old English dæg "day," originally "the heat;" Greek tephra "ashes;" Lithuanian dāgas "heat," Old Prussian dagis "summer;" Middle Irish daig "fire"); but some suggest a reduplication of a root represented by Sanskrit *bhur- "to be restless."
The Latin word was adopted into most of the Germanic languages (German Fieber, Swedish feber, Danish feber), but not Dutch. English spelling was influenced by Old French fievre.
An alternative word for "fever" was Old English hrið, hriðing (which is cognate with Old High German hritto, Irish crith, Welsh cryd, Lithuanian skriečiù, skriesti); Latin febris also was glossed by bryneadl. The extended sense of "intense nervous excitement" is from 1580s. Also as a verb in Old English, feferian.
People are apt to sneeze, in hot weather for example; and people do not die of sneezing now-a-days, as they did in days that no one knows any thing about. We cannot give six draughts a-day, at one and nine pence each, for sneezing: call it the hay-fever. What a wonderful man! what a clever man! he understands the hay-fever: call him in! Thus is the hay-fever among the last in the list of fashionables. ["On Fashions in Physic," London Magazine, October 1825]
1650s, from Medieval Latin febrilis "pertaining to fever," from Latin febris "a fever" (see fever).
c. 1300, "acute fever," also (late 14c.) "malarial fever (involving episodes of chills and shivering)" from Old French ague "acute fever," from Medieval Latin (febris) acuta "sharp (fever)," from fem. of acutus "sharp" (from PIE root *ak- "be sharp, rise (out) to a point, pierce").
"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.
"medicine that reduces fever," 1680s, from French fébrifuge, literally "driving fever away," from Latin febris (see fever) + fugare "cause to flee, put to flight, drive off, chase away, rout," also used in reference to banishment and exile, derived verb from fuga "flight," from PIE *bhug-a-, suffixed form of root *bheug- (1) "to flee" (see fugitive (adj.)).