In a manner filled with or expressing fear; done with dread or apprehension.
From 'feared' (past tense adjective form) plus the adverbial suffix '-ly.' This is a constructed adverb that follows standard English patterns of forming adverbs from adjectives.
This adverb is technically valid but sounds awkward to modern ears because 'fearfully' performs the same function so much more smoothly—it's a reminder that not every grammatically possible word becomes actually used.
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