A Word A Day : Dubious
Dubious (DOO bee us) adj: full of doubt; uncertain
I was fairly certain that I would be able to fly if I could merely flap my arms hard enough, but Mary wad dubious. She said I had better flap my legs as well.
We were dubious about the team's chance of success and, as it turned out, our dubiety was justified, the team lost.
Dubious and doubtful don't mean exactly the same thing. A dubious person is a Person who has doubts. A doubtful outcome is an outcome that isn't certain to occur.
Sam's chances of getting the job were doubtful, because the employer was dubious of his claim that he had been president of the United States while in high School.
Something beyond doubt is indubitable. A dogmatic person believes his opinions are indubitable.