'Unbeliever' in the Bible

But to the rest I say, not the Lord, that if any brother has a wife who is an unbeliever, and she consents to live with him, he must not divorce her.

But if all prophesy, and an unbeliever or an ungifted man enters, he is convicted by all, he is called to account by all;

Or what harmony has Christ with Belial, or what has a believer in common with an unbeliever?

But if anyone does not provide for his own, and especially for those of his household, he has denied the faith and is worse than an unbeliever.