(historical) Black bile, formerly thought to be one of the four "cardinal humours" of animal bodies.
Melancholy, cold and dry, thick, black, and sour, […] is a bridle to the other two hot humours, blood and choler, preserving them in the blood, and nourishing the bones.
Great sadness or depression, especially of a thoughtful or introspective nature.
As to Ernest... He is quite as nervously broken down as I am but it manifests itself in different ways. His inclination is towards megalomania and mine towards melancholy.
adjective
(literary) Affected with great sadness or depression.