In a credent manner; with belief or credulousness; in a way that inspires or gives credence.
From 'credent' (believing or worthy of belief) with the adverbial suffix '-ly.' Very rare in English documentation.
Adverbs like 'credently' show how English word-building rules allow theoretically infinite combinations—you can add '-ly' to almost any adjective, but only the useful ones survive in actual language!
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