concludingly

Quoted in SIR KENELME DIGBY,—II. His Writings in The Gentleman's Magazine, Volume 183 (Volume XXIX New Series, June 1848), page 603, as:

And, … let me recommend to you not onely to examine whether the opinion you meet with in your reading, repugnant to what you were formerly imbued with, be concludingly demonstrated or no, but likewise examine as strictly the reason you have for your own; and when the scale weighs heaviest give your assent.

Quoted by Samuel Johnson in A Dictionary of the English Language (London, 1755) in support of his definition of concludingly as "with uncontrovertible evidence" as:

Examine whether the opinion you meet with, repugnant to what you were formerly embued with, be concludingly demonstrated or not. Digby

This appears to be the basis of many online citation, which fail to identify "Digby" more closely.