A name given now to a habit of feeling, now to a system of opinion; as the former it denotes a tendency to dwell on the dark or gloomy side of things, culminating in a sense of their vanity and nothingness, while in the latter it is applied to all systems of opinion which lay the finger on some black spot in the structure of the life of the world or of the universe, which so long as it remains is thought to render it unworthy of existence.