Noah Webster
Unbelief
UNBELIE'F, noun
1. Incredulity; the withholding of belief; as, unbelief is blind.
2. Infidelity; disbelief of divine revelation.
3. In the New Testament, disbelief of the truth of the gospel, rejection of Christ as the Savior of men, and of the doctrines he taught; distrust of God's promises and faithfulness, etc. Matthew 13:58. Mark 16:14. Hebrews 3:12. Romans 4:20.
4. Weak faith. Mark 9:24.