In a playful and cheerful manner; in a way that shows lighthearted fun and enjoyment.
From 'frolicsome' + adverbial suffix '-ly'. This adverb form allows the quality of playfulness to modify verbs and other words, showing when or how something is done in a frolicsome manner.
Adding '-ly' to adjectives is one of English's most productive tricks, but 'frolicsomely' is special because it manages to sound fun just saying it—the word itself practically bounces off your tongue.
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