Strong's G570 — ἀπιστία (noun)
apistia (ap-is-tee'-ah) n.
1. faithlessness
2. (negatively) disbelief (lack of Christian faith)
3. (positively) unfaithfulness (disobedience)
[from G571]
KJV: unbelief 
Root(s): G571 
Hebrew root: ἄπιστος
Occurrences: 11