In a foppish manner; in a way that shows excessive, foolish concern with appearance and fashion.
From foppish + -ly (adverbial suffix). This is the standard modern way to form adverbs from adjectives in English.
The evolution from fopperly to foppishly shows how English standardized its adverb formation—we moved from multiple options to one clear rule (-ish adjectives + -ly adverbs).
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