In a manner full of chance, risk, or uncertainty; in an unpredictable way dependent on fortune.
From chanceful + -ly (adverbial suffix). This represents a three-layer suffix construction: chance + -ful + -ly, each building on the previous.
The word 'chancefully' is almost Shakespearean in flavor—modern English has abandoned these layered adverbial forms in favor of simple constructions, making old words like this sound poetic by comparison.
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