1. The disbelief in any claims of ultimate knowledge.
2. A doubt about the truth of something.
3. A doubting or questioning attitude or state of mind; dubiety.
4. In philosophy, the ancient school of Pyrrho of Elis who stressed the uncertainty of our beliefs in order to oppose dogmatism.
5. The doctrine that absolute knowledge is impossible, either in a particular domain or in general.
6. A methodology based on an assumption of doubt with the aim of acquiring approximate or relative certainty.
7. Doubt or disbelief of religious tenets.
8. Etymology: from Latin scepticus, which came from Greek skeptikos; from skeptesthai, "to reflect, to look, to view".