1. (n.) An undecided, inquiring state of mind; doubt; uncertainty\.

2. (n.) The doctrine that no fact or principle can be certainly known; the tenet that all knowledge is uncertain; Pyrrohonism; universal doubt; the position that no fact or truth, however worthy of confidence, can be established on philosophical grounds; critical investigation or inquiry, as opposed to the positive assumption or assertion of certain principles.

3. (n.) A doubting of the truth of revelation, or a denial of the divine origin of the Christian religion, or of the being, perfections, or truth of God.

Humism Pyrrhonism agnosticism apprehension caution cautiousness concern diffidence disinclination to believe distrust distrustfulness doubt doubtfulness dubiety dubiousness guardedness half-belief incertitude inconvincibility incredulity leeriness misdoubt misgiving mistrust mistrustfulness qualm qualmishness question resistiveness to belief scoffing scruple scrupulousness self-doubt shadow of doubt skepticalness suspicion suspiciousness total skepticism tough-mindedness uncertainty unconvincibility uncredulousness unpersuadability unpersuasibility wariness wonder