In an old-fashioned, ancient, or antique manner; in the style or way of something from an earlier time.
From antique (adjective) plus the adverbial suffix -ly. Follows the standard pattern of converting adjectives into adverbs in English.
When you add -ly to adjectives, you're describing HOW something happens. 'Antiquely' means doing something the OLD WAY—it's how a Victorian novelist might describe someone stubbornly refusing to use electricity.
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