The superlative form of dun, meaning the most dull grayish-brown color or the most dull in appearance.
From Old English 'dunn', related to Old Norse 'dokkr' meaning dark. The superlative -est was added following standard English grammar patterns. The word has been used since medieval times to describe drab, grayish-brown tones.
Medieval dyers and weavers developed the term 'dun' to describe one of the most common cloth colors they could produce cheaply—it's basically the color of undyed wool, which is why it became synonymous with plain, ordinary, and unremarkable.
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