Strong's G569 — ἀπιστέω (verb)
apisteo (ap-is-teh'-o) v.
1. to be unbelieving
2. (transitively) disbelieve
3. (by implication) disobey
[from G571]
KJV: believe not 
Root(s): G571 
Hebrew root: ἄπιστος
Occurrences: 8