the world > matter > light > darkness or absence of light > darkness or gloom > [adjective] > dim, dark, or obscure > darkening or obscuring (6)
That obscures; covering, concealing.
Of mist, haze, etc.: obscuring, concealing.
That overcasts something (in various senses of the verb).
That darkens or obscures.
Causing or producing darkness; obscuring. (In quot. 1786 loosely for ‘dark, gloomy’.)