Is it ensure, insure, or assure?
late 14c., idroforbia, a symptom of rabies in man (sometimes used for the disease itself), from Late Latin hydrophobia (Celsius, 50 C.E.), from Greek hydrophobos "dreading water," from hydr-, stem of hydros "water" (see water (n.1)) + phobos "dread, fear" (see phobia). So called because human sufferers show aversion to water and have difficulty swallowing it.
hydrophobia hy·dro·pho·bi·a (hī'drə-fō'bē-ə)
An abnormal fear of water.
Our Living Language : Hydrophobia is an older term for the disease rabies, and it means "fear of water." Because of this name, many people think that rabies makes one afraid of water. In fact, this is not the case (although rabies does cause mental confusion of other kinds). The name hydrophobia comes from the fact that animals and people with rabies get spasms in their throat muscles that are so painful that they cannot eat or drink, and so will refuse water in spite of being very thirsty.