Definitions for: Darkening

[n] changing to a darker color
[adj] becoming dark or darker as from waning light or clouding over; "the darkening sky"

Webster (1913) Definition: Dark"en*ing, n.
Twilight; gloaming. [Prov. Eng. & Scot.] --Wright.

Synonyms: blackening, dark

See Also: change of color, obfuscation