Abbott-Smith Manual Greek Lexicon
ἄ-πιστος (G571)
23 ἄ-πιστος , -ον ( ἀ- neg., πιστός ), [in LXX: Pr 17:6 28:25 , Is 17:10 *;] of things, incredible : Ac 26:8 ; of persons, without faith or trust , unbelieving : Mt 17:17 , Mk 9:19 , Lk 9:41 12:46 , Jo 20:27 , Tit 1:15 , Re 21:8 ; specif., of unbelievers as opp. to Christians: I Co 6:6 7:12-15 10:27 14:22-24 , II Co 4:4 6:14 , 15 , I Ti 5:8 (cf. Lft., Notes , 265; Cremer, 491).†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain