In a manner that glistens; shining softly or sparkling with reflected light in a characteristic way.
From 'glisten' + '-ing' (present participle) + '-ly' (adverbial suffix). This creates an adverb from an adjective form, following standard English morphology for converting verbs into manner adverbs.
Adverbs like 'glisteningly' are rare in modern English because they're considered poetic or overwrought—yet they appear regularly in fantasy literature and romantic poetry where writers want to emphasize persistent, shimmering beauty as a characteristic quality.
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