In a manner that shows agreement, harmony, or concord with others.
From agreeing (present participle of agree) + -ly (adverbial suffix). This forms an adverb from the gerund/participle form rather than the adjective.
While 'agreeably' is common, 'agreeingly' is much rarer—it emphasizes the action of agreeing rather than the pleasant quality of something. It's the kind of word you might see in poetry or philosophical writing where precise gradations matter.
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