To become dusk or grow dark; to make something darker or cause it to approach darkness.
From 'dusk' with the verb-forming suffix '-en' (as in 'darken,' 'lighten,' 'widen'). This creates a verb meaning 'to become dusky' or 'to make dusky,' following standard English word-building patterns.
This verb shows how flexible English is—we can turn almost any adjective into a verb by adding '-en,' and 'dusken' is a beautiful example that poets have used to describe the gradual onset of twilight.
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