ἀπιστία

Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God.

So we see that they could not enter in because of unbelief.

Who was before a blasphemer, and a persecutor, and injurious: but I obtained mercy, because I did it ignorantly in unbelief.

And he marvelled because of their unbelief. And he went round about the villages, teaching.

And straightway the father of the child cried out, and said with tears, Lord, I believe; help thou mine unbelief.

Afterward he appeared unto the eleven as they sat at meat, and upbraided them with their unbelief and hardness of heart, because they believed not them which had seen him after he was risen.

And he did not many mighty works there because of their unbelief.

And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.

For what if some did not believe? shall their unbelief make the faith of God without effect?

He staggered not at the promise of God through unbelief; but was strong in faith, giving glory to God;