fever (n.) Look up fever at Dictionary.com
late Old English fefor, fefer "fever," from Latin febris "fever," related to fovere "to warm, heat," probably from PIE root *dhegh- "burn" (cognates: Gothic dags, Old English dæg "day," originally "the heat;" Greek tephra "ashes"); but some suggest a reduplication of a root represented by Sanskrit *bhur- "to be restless."

The Latin word was adopted into most Germanic languages (German Fieber, Swedish feber, Danish feber), but not in Dutch. English spelling influenced by Old French fievre. Replaced Old English hriðing. Extended sense of "intense nervous excitement" is from 1580s.