Quick Definition
ἄπιστος, ον Adj unbelieving, incredulous, unchristian, unbeliever
Strong's Definition
from 1 (as a negative particle) and 4103; (actively) disbelieving, i.e. without Christian faith (specially, a heathen); (passively) untrustworthy (person), or incredible (thing)
KJV Usage: that believeth not, faithless, incredible thing, infidel, unbeliever(-ing)
UBS Dictionary of the Greek New Testament
adjc. | -ον | ἀ- + πιστεύω
31.40 · Hold a View, Believe, Trust · Believe To Be True
unbelievable, impossible to be believed (derivative of ἀπιστέω[a] ‘to not believe,’ 31.39) pertaining to not being believable
adjc. | -ον | ἀ- + πιστεύω
31.106 · Hold a View, Believe, Trust · Be a Believer, Christian Faith
one who is not a believer, unbeliever one who does not believe the good news about Jesus Christ It is clearly not enough in most languages to render ἄπιστος[b] in MRK 9:19 (see 31.98).
MRK 9:19 · 1CO 6:6 · 1CO 10:27 · 1CO 14:22 · 1CO 14:22 · 2CO 4:4 · 2CO 6:15 · 1TI 5:8 · REV 21:8
11.19 · Groups and Classes of Persons and Members of Such Groups and Classes · Socio-Religious
non-Christian a person who does not belong to the group of believers in Christ In 1CO 7:15 it may be necessary to indicate the so-called goal of belief or trust, for example, ‘if one who is not a believer in Christ’ or ‘if the one who is not a follower of Christ.’
1CO 7:12 · 1CO 7:13 · 1CO 7:14 · 1CO 7:14 · 1CO 7:15 · 1CO 10:27 · 1CO 14:22 · 1CO 14:22 · 1CO 14:23 · 1CO 14:24 · 2CO 6:14
1 The problems of classifying ἄπιστος are essentially similar to those involving πιστή[b] (= πιστός[e]; 11.17 and footnote).
UBS Dictionary of the Greek New Testament © United Bible Societies, licensed CC BY-SA 4.0.
Thayer's Greek Lexicon
ἄπιστος, -ov, (πιστός), [fr. Hom. down], without faith or trust; 1. unfaithful, faithless, (not to be trusted, perfidious): Lk. xii. 46; Rev. xxi.8. 2. incredible, of things: Acts xxvi. 8; (Xen. Hiero 1, 9; symp. 4, 49; Cyr. 3,1, 26; Plat. Phaedr. 245 c.; Joseph. antt. 6, 10, 2, ete.). 3. unbelieving, incredulous: of Thomas disbelieving the news of the resurrection of Jesus, Jn. xx. 27; of those who refuse belief in the gosnel, 1 Co. vi. 6; vii. 12-15; x. 27; xiv. 22 sqq.; [1 Tim. v. 8]; with the added idea of impiety and wickedness, 2 Co. iv. 4; vi. 14 sq. of those among the Christians themselves who reject the true faith, Tit. i. 15. without trust (in God), Mt. xvii. 17; Mk. ix.19; Lk. ix. 41." ἁπλότης, -ητος, 7, singleness, simplicity, sincerity, mental honesty; the virtue of one who is free from pretence and dissimulation, (so in Grk. writ. fr. Xen. Cyr. 1, 4, 3; Hell. 6,1,18,down): ἐν ἁπλότητι (1, Τ Tr WH ἁγιόTTL) καὶ εἰλικρινείᾳ θεοῦ i. 6. infused by God through the Spirit [W. § 36, 3 b.], 2 Co. i. 12; ἐν ἅπλ. τῆς καρδίας (229 Ww, 1 Chr. xxix. 17), Col. iii. 22; Eph. vi. 5, (Sap. i. 1); εἰς Χριστόν. sincerity of mind towards Christ, i. e. single-hearted faith in Christ, as opp. to false wisdom in matters pertaining to Christianity, 2 Co. xi.3; ἐν ἁπλότητι in simplicity, i. 6. without self-seeking, Ro. xii. 8. openness of heart manifesting itself by benefactions, liberality, (Joseph. antt. 7, 13,4; but in opposition see Fritzsche on Rom. vol. iii. 62 sq.]: 2 Co. viii. 2; ix. 11, 13 (τῆς κοινωνίας, manifested by fellowship). Cf. Kling s. v. ‘ Einfalt’ in Herzog iii. p. 723 sq.
Mounce Concise Greek Dictionary
ἄπιστος apistos 23x
unbelieving, without confidence in any one, Mt. 17:17; violating one’s faith, unfaithful, false, treacherous, Lk. 12:46; an unbeliever, infidel, pagan, 1 Cor. 6:6; pass. incredible, Acts 26:8
Abbott-Smith Greek Lexicon
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).†
Moulton & Milligan — Vocabulary of the Greek NT
ἄπιστος may be cited from Sy// 80 253 (iii/B.c.) meaning first “incredible” and then ‘‘incredulous” : ὅτι τοίνυν ἔμπροσθεν ἀπιστεῖς avro[ts] (the inscriptions recording cures), οὐκ ἐοῦσιν ὀπίστοις, τὸ λοιπὸν ἔστω τοι, φάμεν, "Απιστος ὄν[ομα]. It is MGr.
Liddell-Scott-Jones — Greek-English Lexicon
ἄπιστος (apistos) — unbelieving. ἄπιστος, ον,
I. passive, not to be trusted, and so:
I.1. of persons and their acts, not trusty, faithless, ὑπερφίαλοι καὶ ἄ.[Refs 8th c.BC+]; δολοπλοκίαι[Refs 6th c.BC+]mistrusted, [Refs 5th c.BC+]; θράσει ἀ. ἐπαιρόμενος by untrustworthy, groundless confidence, [Refs 5th c.BC+]; shifty, unreliable, [Refs 5th c.BC+]
I.2. of reports and the like, incredible, uncertain in [Refs 7th c.BC+]; τὸ ἐλπίδων ἄ. undreamed of even in hope, [Refs 5th c.BC+]: comparative -ότερος, λόγος[Refs 4th c.BC+]: superlative, πίστις ἀπιστοτάτη[Refs 5th c.BC+]
II. active, mistrustful, incredulous, suspicious, θυμὸς δέ τοι αἰὲν ἄ.[Refs 8th c.BC+]less credulous, [Refs 5th c.BC+]; ἄ. πρὸς Φίλιππον distrustful towards him, [Refs 4th c.BC+]; ἄ. εἶ.. σαυτῷ you do not believe what you say yourself, [Refs 5th c.BC+]; τὸ ἄ., ={ἀπιστία}, [Refs 5th c.BC+]
II. b in NT, unbelieving, [NT]
II.2. disobedient, disloyal, [Refs 5th c.BC+]; ἔχειν ἄπιστον.. ἀναρχίαν πόλει, i.e. ἀναρχίαν ἔχειν ἀπειθοῦσαν τῇ πόλει,[Refs 5th c.BC+]
III. adverb ἀπίστως:
III.1. passive, beyond belief, ἀ. ἐπὶ τὸ μυθῶδες ἐκνενικηκότα[Refs 5th c.BC+]; οὐκ ἀ. not incredibly, [Refs 4th c.BC+]
III.2. active, distrustfully, suspiciously, [Refs 5th c.BC+]
III.2. b treacherously, [Refs 1st c.AD+]