undoubtingly

undoubting +‎ -ly

undoubtingly (comparative more undoubtingly, superlative most undoubtingly)

1. Without doubting.
   • 1659, John Pearson, An Exposition of the Creed, London: J. Williams, 6th edition, 1692, Article VIII, p. 316,

     But were there nothing, which is already said, demonstrated, there is enough written in the Word of God to assure us of the Deity of the Holy Ghost, to make us undoubtingly believe that the Spirit of God is God.

   • 1753, Samuel Richardson, The History of Sir Charles Grandison, London: Harrison & Co., 1785, Volume 4, Letter 14, p. 525

     Poor Mr. Orme! I am sorry he is not well. It is cruel in you, Lucy, at this time, to say (so undoubtingly) that his illness is owing to his love of me.

   • 1811, Jane Austen, Sense and Sensibility, Chapter 5,

     […] she relied so undoubtingly on Sir John’s description of the house, as to feel no curiosity to examine it herself till she entered it as her own.

   • 1859, John Stuart Mill, On Liberty, Chapter 2,

     There is a class of persons (happily not quite so numerous as formerly) who think it enough if a person assents undoubtingly to what they think true, though he has no knowledge whatever of the grounds of the opinion, and could not make a tenable defence of it against the most superficial objections.