Asseverate

Whereas Your Maiesty hath received true information of great sums of Money endeavoured to be borrowed of Your City of London, by directions proceeding from both Houses of Parliament […] (I Your Maiesties faithfull Subiect) doe conceive, and dare asseverate, that it is intended upon no other pretence then for the Honour and defence of Your Maiesty,

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I will myself asseverate and bind it by an Oath, that the Muff thou bearest in thy Hand belonged unto Madam Sophia;

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“And I presume you can also asseverate to his worship, that no man is better qualified than I am to bear testimony in this case, seeing that I was by you, and near you, constantly during the whole occurrence?”

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The more I laughed at such theories, the more these stubborn friends asseverated them; adding that even without the heritage of legend the recent reports were too clear, consistent, detailed, and sanely prosaic in manner of telling, to be completely ignored.

Source: wiktionary