In a sweet manner; done kindly, pleasantly, or with a pleasant taste or sound.
From Old English 'swete' (sweet) plus the adverbial suffix '-ly', which transforms adjectives into adverbs. The root 'swete' comes from Proto-Germanic and is related to words meaning 'pleasant to taste.'
The suffix '-ly' is one of English's most productive word-building tools—it can turn almost any adjective into an adverb, which is why we can sweetly describe something being done in a sweet way, but we can also 'sweetly' manipulate someone by being deceptively kind.
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