In an extravagant manner; with excessive spending, flamboyant style, or behavior that exceeds all reasonable limits.
From 'extravagant' + '-ly' (adverbial suffix), itself from Medieval Latin 'extravagans' (wandering beyond), creating an adverb describing actions performed in an excessive way.
When someone dresses 'extravagantly,' they're taking fashion way beyond what's necessary or sensible—historians use this word to describe Renaissance kings spending fortunes on increasingly absurd costumes and jewels.
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