In a confirmatory manner; in a way that serves to confirm or verify something.
From 'confirmatory' (adjective) plus the adverb suffix '-ly.' This creates a double-suffix formation, which is typical for adverbs derived from '-atory' adjectives in English.
The existence of both 'confirmatively' and 'confirmatorily' shows the redundancy that builds up in English—we create multiple adverb forms from related adjectives, and speakers naturally prefer one over the other based on how it sounds and feels in context.
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