undoubtful en · ADJ
Etymology
From un- + doubtful.
Meanings
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(not-comparable) Not doubtful.
I was utterly unconscious of this irregularity, and might have remained so, had not a friend the next day asked me the reason of it. Indeed I should have disbelieved that it had taken place, had not the testimony of several persons rendered it undoubtful.
1844, William Clowes, The Journals of William Clowes: A Primitive Methodist Preacher: