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Study Dictionary
Infidel
INFIDEL [ISBE]
INFIDEL - in'-fi-del (apistos, "unbelieving," "incredulous"): the King James Version has this word twice: "What part hath he that believeth with an infidel?" (2 Cor 6:15); "If any provide not for his own, .... is worse than an infidel" (1 Tim 5:8). In both passages the English Revised Version and the American Standard Revised Version have "unbeliever" in harmony with numerous other instances of the use of the Greek apistos. The word nowhere corresponds to the modern conception of an infidel, one who denies the existence of God, or repudiates the Christian faith; but always signifies one who has not become a believer in Christ. It was formerly so used in English, and some of the older versions have it in other passages, besides these two. It is not found in the Old Testament, but "infidelity" (incredulity) occurs in 2 Esdras 7:44 (114).William Owen Carver
Also see definition of "Infidel" in Word Study