An unbeliever is somebody who does not believe.
Matthew 13:58 And he did not many mighty works there because of their unbelief.
Matthew 17:20 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.
Mark 6:6 And he marvelled because of their unbelief. And he went round about the villages, teaching.
Mark 9:24 And straightway the father of the child cried out, and said with tears, Lord, I believe; help thou mine unbelief.
Mark 16:14 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.
Romans 3:3 For what if some did not believe? shall their unbelief make the faith of God without effect?
Romans 4:20 He staggered not at the promise of God through unbelief; but was strong in faith, giving glory to God;
Romans 11:20 Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear:
Romans 11:23 And they also, if they abide not still in unbelief, shall be graffed in: for God is able to graff them in again.
Romans 11:30 For as ye in times past have not believed God, yet have now obtained mercy through their unbelief:
Romans 11:32 For God hath concluded them all in unbelief, that he might have mercy upon all.
1 Timothy 1:13 Who was before a blasphemer, and a persecutor, and injurious: but I obtained mercy, because I did it ignorantly in unbelief.
Hebrews 3:12 Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God.
Hebrews 3:19 So we see that they could not enter in because of unbelief.
Hebrews 4:6 Seeing therefore it remaineth that some must enter therein, and they to whom it was first preached entered not in because of unbelief:
Hebrews 4:11 Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief.
Luke 12:46 The lord of that servant will come in a day when he looketh not for him, and at an hour when he is not aware, and will cut him in sunder, and will appoint him his portion with the unbelievers.
1 Corinthians 6:6 But brother goeth to law with brother, and that before the unbelievers.
1 Corinthians 14:23 If therefore the whole church be come together into one place, and all speak with tongues, and there come in those that are unlearned, or unbelievers, will they not say that ye are mad?
2 Corinthians 6:14 Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?