In a cheerful, bright, or lively manner; in the manner of someone or something that chirps.
From 'chirpy' + '-ly' (adverb suffix). The '-ly' ending, from Old English 'lic' (like, resembling), transforms adjectives into adverbs indicating manner or quality.
The '-ly' adverb suffix is so productive in English that we can turn almost any adjective into an adverb describing how something is done, and non-native speakers instinctively understand new adverbs they've never heard because they recognize the pattern—that's the power of transparent word formation.
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