"rage, madness, angry mania," late 15c., furour, from Old French fureur (12c.), from Latin furor "a ravaging, rage, madness, passion," which is related to furia "rage, passion, fury" (see fury).
c. 1300, "madness, insanity; fit of frenzy; rashness, foolhardiness, intense or violent emotion, anger, wrath; fierceness in battle; violence" (of storms, fire, etc.), from Old French rage, raige "spirit, passion, rage, fury, madness" (11c.), from Medieval Latin rabia, from Latin rabies "madness, rage, fury," related to rabere "be mad, rave" (compare rabies, which originally had this sense). This is said by some sources to be from PIE *rebh- "violent, impetuous" (source also of Old English rabbian "to rage"), but de Vaan finds this uncertain and sees no convincing etymology.
Similarly, Welsh (cynddaredd) and Breton (kounnar) words for "rage, fury" originally meant "hydrophobia" and are compounds based on the word for "dog" (Welsh ci, plural cwn; Breton ki).
It is attested from late 14c. in the sense of "fit of carnal lust or sexual desire." In 15c.-16c. it also could mean "rabies." Other Middle English senses, now obsolete, include "come to a boil; grieve, mourn, lament; flirt, make love." The rage "fashion, vogue" dates from 1785.
"extremely fatal infectious disease of dogs, humans, and many other mammals," 1590s, from Latin rabies "madness, rage, fury," related to rabere "be mad, rave" (see rage (v.)). The mad-dog disease sense was a secondary meaning of the Latin noun. Known as hydrophobia (q.v.) in humans. Related: Rabietic.