Made black or blackened, especially with soot or coal dust; darkened.
From the verb 'colly,' which comes from Middle English and likely relates to coal or soot; the past tense form suggests something that has been darkened or made black.
Shakespeare used 'collied' in 'A Midsummer Night's Dream' to describe how night blackens the sky—it's a poetic old word that captures the feeling of things getting darkened by darkness itself!
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