In a worried, anxious, or fretful manner; while fretting or worrying.
From 'fret' + present participle '-ing' + adverbial suffix '-ly', creating an adverb that describes how an action is performed.
The '-ly' adverbial suffix is so common we barely notice it, but it's actually a contraction of Old English 'like'—so 'frettingly' literally means 'in a fret-like way.'
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