In a manner that is good-natured, willing, or done with good intentions.
From 'goodwill' plus the adverbial suffix '-y' or '-ly', creating an archaic adverb form meaning 'in a manner of good will.' This represents an older way of forming adverbs before Modern English standardized most -ly formations.
English speakers once added '-ly' to noun phrases much more freely than we do now—'goodwily' shows how the language gradually shifted toward using standardized prepositions ('with good will') instead of creating new adverbs.
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