Unbeliever
Vine's Expository Dictionary of NT Words [1]
an adjective, is used as a noun, rendered "unbeliever" in 2 Corinthians 6:15; 1 Timothy 5:8 , Rv; plural in 1 Corinthians 6:6; 2 Corinthians 6:14; Av only, Luke 12:46 (Rv, "unfaithful"). See Belief , C, Note (3) Faithless, Incredible.
Morrish Bible Dictionary [2]
ἄπιστος.The name given in scripture to the class of persons who have not faith in the divine revelation of the gospel. Luke 12:46; 1 Corinthians 6:6; 1 Corinthians 14:23; 2 Corinthians 6:14 . The word is translated 'infidel' in 2 Corinthians 6:15; 1 Timothy 5:8; and 'faithless' in Matthew 17:17; Mark 9:19; Luke 9:41; John 20:27 .
Webster's Dictionary [3]
(1): ( n.) One who does not believe; an incredulous person; a doubter; a skeptic.
(2): ( n.) A disbeliever; especially, one who does not believe that the Bible is a divine revelation, and holds that Christ was neither a divine nor a supernatural person; an infidel; a freethinker.
International Standard Bible Encyclopedia [4]
un - bḗ - lēv´ẽr : This word follows closely the lines of "unbelief" (which see) in its relation to originals. Once only ( Acts 14:2 ) it represents the participle ἀπειθοῦντες , apeithoúntes , "disobeying (ones)." Elsewhere (nine cases) it represents ἄπιστος , ápistos , "faithless," "without faith." In six of these passages (all in 1 and 2 Corinthians) it denotes the unconverted pagan as distinguished from the convert. In the other passages ( Luke 12:46; Titus 1:15; Revelation 21:8 ) the reference is to the unbelief which comes of moral resistance to God.