Similar words: slackening, blacken, blackened, sickening, thickening, quickening, sickeningly, slacken. Meaning: ['blækən] 
n. changing to a darker color.
n. changing to a darker color. 
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31. In the spring fire swept across the hills, blackening them.
32. The output signal from the detector may be the blackening of a photographic emulsion.
More similar words: slackening, blacken, blackened, sickening, thickening, quickening, sickeningly, slacken, black eye, slacken off, black economy, wakening, awakening, weakening, darkening, blacking, black pudding, black jack, blackjack, black, back end, bracken, broken in, blackout, black out, lacker, lackey, blacktop, jet-black, jet black.