undoubting

un- +‎ doubting

undoubting (not comparable)

1. (of persons, states of mind, beliefs, etc.) Experiencing or harboring no doubts; entirely confident.
   • 1665, George Wither, Meditations on the Lord's Prayer, London, page 75:

     And we shall have an undoubting assurance that that this Kingdom is in such a measure within us, as will ripen to perfection in due time.

   • 1787, Jonathan Edwards, Treatise concerning the religious affections, New York, N.Y.: Robert Hodge, page 196:

     And God's declared design in all this is, that the heirs of the promises might have an undoubting hope.

   • 1814 July, [Jane Austen], chapter IV, in Mansfield Park: A Novel. In Three Volumes, volume II, London: Printed for T[homas] Egerton, […], OCLC 39810224, page 88:

     With undoubting decision she directly began her adieus; […]

   • 1919, Virginia Woolf, chapter XXIV, in Night and Day:

     It was the part of a gentleman to preserve a bearing that was, as far as he could make it, the bearing of an undoubting lover.

   • 2002 October 6, Mike Greenberg, “Guest, symphony an adept team”, in San Antonio Express-News, page 8B:

     This overstuffed, smug, showy and sentimental music can almost persuade when it is performed with undoubting conviction.

• undoubtingly

• undoubting in An American Dictionary of the English Language, by Noah Webster, 1828.
• Oxford English Dictionary, 2nd ed., 1989.
• Random House Webster's Unabridged Electronic Dictionary, 1987-1996.