'Melancholia' would still appear to be a far more apt and evocative word for the blacker forms of the disorder, but it was usurped by a noun with a bland tonality and lacking any magisterial presence, used indifferently to describe an economic decline or a rut in the ground, a true wimp of a word for such a major illness.
William Styron, Darkness Visible: A Memoir of Madness