Not settled in opinion; undetermined; wavering; hesitating in belief; also used, metaphorically, of the body when its action is affected by such a state of mind; as, we are doubtful of a fact, or of the propriety of a measure.
Admitting of doubt; not obvious, clear, or certain; questionable; not decided; not easy to be defined, classed, or named; as, a doubtful case, hue, claim, title, species, and the like.
Characterized by ambiguity; dubious; as, a doubtful expression; a doubtful phrase.
A civilized society is one which tolerates eccentricity to the point of doubtful sanity. Robert Frost
Life is like music, it must be composed by ear, feeling and instinct, not by rule. Nevertheless one had better know the rules, for they sometimes guide in doubtful cases, though not often. Paracelsus
The tendency of modern scientific teaching is to neglect the great books, to lay far too much stress upon relatively unimportant modern work, and to present masses of detail of doubtful truth and questionable weight in such a way as to obscure principles. Ronald Fisher
A doubtful friend is worse than a certain enemy. Let a man be one thing or the other, and we then know how to meet him. Aesop
I cannot explain it; but when difficulties arise, I am not perplexed or doubtful. I know how to meet them. Anne Sullivan