To sully or defame: a scandal that blackened the mayor's name.
To coat (fish or meat, for example) with pepper and other spices and then quickly sear in a very hot skillet, thereby producing meat that is black on the outside but tender on the inside.
intransitive verb
To become dark or black: The day blackened into night.
derivatives
blacḱen·er
noun
The American Heritage® Dictionary of the English Language, Fourth Edition