In a debonaire manner; with suave, elegant, and gracious bearing or speech.
From the adjective 'debonaire' with the adverbial suffix '-ly' (from Old English 'lic' meaning 'like' or 'in the manner of'). This creates the standard English pattern for converting adjectives to adverbs.
The '-ly' suffix is one of English's greatest recycling programs—it comes from the word 'like' and turns any adjective into an adverb that means 'in the manner of that adjective,' giving us thousands of adverbs from just one tiny suffix.
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