skepticism

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A doubting or questioning attitude or state of mind; dubiety. See Synonyms at uncertainty.
2. n. Philosophy The ancient school of Pyrrho of Elis that stressed the uncertainty of our beliefs in order to oppose dogmatism.
3. n. Philosophy The doctrine that absolute knowledge is impossible, either in a particular domain or in general.
4. n. Philosophy A methodology based on an assumption of doubt with the aim of acquiring approximate or relative certainty.
5. n. Doubt or disbelief of religious tenets.

Century Dictionary and Cyclopedia

1. n. The entertaining of mistrust, doubt, or disbelief; especially, the reasoning of one who doubts the possibility of knowledge of reality; the systematic doubt which characterizes a philosophical skeptic; specifically, doubt or disbelief of the fundamental doctrines of the Christian religion.

Wiktionary

1. n. US The practice or philosophy of being a skeptic.
2. n. US A studied attitude of questioning and doubt
3. n. US The doctrine that absolute knowledge is not possible
4. n. US A methodology that starts from a neutral standpoint and aims to acquire certainty though scientific or logical observation.
5. n. US Doubt or disbelief of religious doctrines

GNU Webster's 1913

1. n. An undecided, inquiring state of mind; doubt; uncertainty.
2. n. (Metaph.) 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. (Theol.) 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.

WordNet 3.0

1. n. the disbelief in any claims of ultimate knowledge
2. n. doubt about the truth of something