Third-person singular simple present indicative form of darken.(verb)
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Use "darkens" in a sentence
"As it is, I do not think I have lost anything, except one's skin darkens from the sun, and one feels weak from the heat; but I could recover in six months in England."
"So, when the lizard is stressed, it's skin darkens and provides greater emphasis for the reflective scales."
"But”—his expression darkens—“Cecil’s spleen is enlarged too."