rabies n.

mid-13c., ragen, "to play, romp," from rage (n.). Original sense now obsolete. Meanings "be furious; speak passionately; go mad" are attested from early 14c. Of things "be violently driven or agitated," from 1530s. Related: Raged; raging.

late 14c., idroforbia, "dread of water, aversion to swallowing water," a symptom of rabies in man (sometimes used for the disease itself), from Late Latin hydrophobia, from Greek hydrophobos "dreading water," from hydr-, stem of hydor "water" (from suffixed form of PIE root *wed- (1) "water; wet") + phobos "dread, fear" (see phobia). So called because human sufferers show aversion to water and have difficulty swallowing it. In Old English as wæterfyrhtness. Related: Hydrophobe.

The term hydrophobia, which has been so generally applied to the Lyssa canina, has been deservedly reprobated, because the "dread of water," the literal meaning of the word, is not a pathognomonic mark of the disease. The older writers used the terms aerophobia, or a "dread of air," and pantophobia, or a "fear of all things," as appropriate names for the disease, because the impression cold air sometimes excites terror, and the disorder is marked, by a singular degree of general timidity and distrust. ["Encyclopaedia Londinensis," 1823]

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.