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