febrifuge n.

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.

late 14c., "fleeing, having fled, having taken flight," from Old French fugitif, fuitif "absent, missing," from Latin fugitivus "fleeing," past-participle adjective from stem of fugere "to flee, fly, take flight, run away; become a fugitive, leave the country, go into exile; pass quickly; vanish, disappear, perish; avoid, shun; escape the notice of, be unknown to," from PIE root *bheug- "to flee" (source also of Greek pheugein "to flee, escape, go into exile, be on the run," phyza "(wild) flight, panic," phyge "flight, exile;" Lithuanian būgstu, būgti "be frightened," bauginti "frighten someone," baugus "timid, nervous;" perhaps also Avestan būj(i)- "penance, atonement," būjat "frees"). Old English had flyma.

Meaning "lasting but a short time, fleeting" is from c. 1500. Hence its use in literature for short compositions written for passing occasions or purposes (1766).