blacken

Etymology

From Middle English blaknen, blakkenen, equivalent to black + -en (verbal suffix).

verb

1. (transitive, causative) To cause to be or become black.
   Iron and coal were the magnets that drew railways to this land of lovely valleys and silent mountains—for such it was a century-and-a-half ago, before man blackened the valleys with the smoke of his forges, scarred the green hills with his shafts and waste-heaps, and drove the salmon from the quiet Rhondda and the murmuring Taff. 1939 September, D. S. Barrie, “The Railways of South Wales”, in Railway Magazine, page 157
2. (intransitive, ergative) To become black.
   The sky blackened as the storm clouds rolled in.
3. (transitive, causative) To make dirty.
4. To defame or sully.
5. (transitive) To cook (meat or fish) by coating with pepper, etc., and quickly searing in a hot pan.