(transitive, causative) To cause to be or become black. / (intransitive, ergative) To become black. / (transitive, causative) To make dirty. / To defame or sully.

present participle of blacken

The act or result of turning black in colour; a black stain or mark. / Any of various (dark-colored) surface treatments for metal substrates, to inhibit corrosion; on steel, generally, synonym of bluing.

Third-person singular simple present indicative form of blacken

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(rare) The quality, state, or condition of being blackened.