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]