The Greek word apistos

Similar to the Greek verb “apisteo” and the Greek noun “apistia,” the Greek adjective “apistos” meant “unbelieving,” “believe not,” “unfaithful,” and “incredible” (unbelievable).  This adjective occurs most often in the book of First Corinthians (6:6; 7:12-15; 10:27; 14:22-24), but it is also used in Matthew, Mark, Luke, John, Acts, Second Corinthians, First Timothy, Titus, and the book of Revelation.

Jesus spoke of a “faithless” generation (Mt. 17:17).  “Unfaithful” people (ASV) will be condemned (Lk. 12:46).  A Christian may be married to an “unbelieving” spouse (1 Cor. 7:13-15).  Christians may have “unbelieving” friends (1 Cor. 10:27).  Satan wants to blind the minds of “unbelievers” (2 Cor. 4:4), and Christians are to avoid being unequally yoked with “unbelievers” (2 Cor. 6:14).  It is possible to be worse than an “unbeliever” (1 Tim. 5:8).  Some regard certain truths about the gospel to be “incredible” (Acts 26:8).