In a manner full of danger; dangerously, though this is an archaic or non-standard adverbial form.
From the rare adjective 'dangerful' plus the adverb-forming suffix '-ly,' creating a doubly archaic form that never achieved standard usage.
This word represents linguistic competition—'dangerously' (from 'dangerous') became standard, while 'dangerfully' lost the race, showing how only certain word-forms survive the evolution of a language.
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