In a manner that expresses agreement or approval; in an assenting way.
Formed from 'assenting' (verb form) plus the adverbial suffix '-ly', which converts adjectives and participles into adverbs describing how an action is performed.
This adverb represents a dying breed of English words—the '-ly' suffix allows speakers to modify any action with a quality of agreement, which explains why you see old texts full of adverbs that modern writers would simply delete.
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