Dictionary.net

A species of melancholia or mental disease under the influence of which the sufferers are led to commit suicide by drowning. It frequently accompanies the last stages of the skin disease called Pellagra (which see).

h[=i]-dro-m[=a]'ni-a, n. an insatiable craving for water, as in diabetes: a morbid propensity to suicide by drowning.

A name given by Stramabi to pellagra, in which the patient has a strong propensity to drown himself.