- The doctrine that certainty about first principles or absolute truth is unattainable and that only perceptual phenomena are objects of exact knowledge.
- The belief that the existence or nonexistence of a deity or deities cannot be known with certainty.
- The view that absolute truth or ultimate certainty is unattainable, especially regarding knowledge not based on experience or perceivable phenomena.
- The view that the existence of God or of all deities is unknown, unknowable, unproven, or unprovable.
- Doubt, uncertainty, or scepticism regarding the existence of a god or gods.
a- + gnostic + -ism