In the manner of a corroborator; in a way that acts to corroborate or confirm something through testimony or evidence.
From 'corroborator' plus '-ily' adverbial suffix, creating a rarely-used adverb describing the manner of acting as a corroborator.
This extraordinarily rare word demonstrates how English can theoretically create adverbs from almost any noun—while 'corroboratorily' appears in few texts, its existence shows the productive power of English word-formation rules.
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