In a way that shows struggle, clumsiness, and difficulty in moving or thinking; without clear direction or purpose.
From 'flounder' plus '-ing' (present participle) plus '-ly' (adverbial suffix). The two-step suffix formation creates an adverb describing the manner of floundering.
Adding '-ingly' to a verb like this (from '-ing' + '-ly') creates adverbs of manner that describe how something happens moment by moment—you're not just floundering, you're doing everything in a floundering way!
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