Noun
The action of darkening or fact of being darkened, as with a cloud; obscuration. [1610]
(medicine, specifically) Obscuration or clouding of the mind or faculties. [1753]
(rare, literally) A veiling with or concealment in clouds. [1814]
Something that obscures or causes confoundment; an obfuscation. [1999]
Source: en.wiktionary.org