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]