indubious

from The Collaborative International Dictionary of English v.0.48

Indubious \In*du"bi*ous\, a. [L. indubius. See {In-} not, and
   {Dubious}.]
   [1913 Webster]
   1. Not dubious or doubtful; certain.
      [1913 Webster]

   2. Not doubting; unsuspecting. "Indubious confidence."
      --Harvey.
      [1913 Webster]