In a manner characterized by deep thought, reflection, or careful consideration; thoughtfully.
From contemplated (past participle of contemplate) plus -ly (adverbial suffix). This creates an adverb emphasizing a thoughtful manner of action.
This is one of those stacked adverbs (contemplat-ed-ly) that sounds formal and slightly archaic—modern writers usually prefer 'thoughtfully' or 'reflectively' instead, showing how shorter, simpler words often win over complex formations.
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