In a manner characterized by unsteady, quick variations in brightness or intensity; with a flickering quality.
From flickering (present participle of flicker) combined with the adverbial suffix -ly, which derives from Old English 'lice' meaning 'like' or 'in the manner of,' allowing adjectives and participles to become adverbs.
The double -ing- in flickeringly creates a delightful tongue-twister that actually mirrors the stuttering, repetitive nature of flickering light itself—the word's form echoes its meaning.
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