Stating something firmly and seriously, often with great emphasis, to convince others it's true.
From Latin 'asseverare' (ad- 'to' + severus 'serious, stern'), meaning to assert earnestly. The word evolved in Middle English to mean emphatic or solemn affirmation of truth.
Before modern fact-checking, 'asseverating' was how people performed certainty—the more dramatically you asseverated, the more convincing you seemed, which is why old literature is full of characters asseverating things that turned out to be completely false!
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