Quick Definition
ἅπαξ Adv once, once for all
Strong's Definition
probably from 537; one (or a single) time (numerically or conclusively)
KJV Usage: once
UBS Dictionary of the Greek New Testament
advb. | ἐφάπαξ
60.67 · Number · Once, Twice, Three Times, Etc. [Cardinals of Time]
once, one time a single occurrence
2CO 11:25 · HEB 9:7 · HEB 9:27 · HEB 9:28 · HEB 10:2 · HEB 12:26 · HEB 12:27 · 1PE 3:18
60.68 · Number · Once, Twice, Three Times, Etc. [Cardinals of Time]
once and for all, once and never again a single occurrence to the exclusion of any other similar occurrence In a number of languages the equivalent of ‘once and for all’ is simply ‘once and not again’ or ‘once and not twice.’
HEB 6:4 · HEB 9:26 · HEB 10:2 · HEB 12:26 · 1PE 3:18 · JUD 1:3 · JUD 1:5
1 It is possible that ἐφάπαξ is somewhat more emphatic in meaning than ἅπαξ, but this cannot be determined from existing NT contexts.
UBS Dictionary of the Greek New Testament © United Bible Societies, licensed CC BY-SA 4.0.
Thayer's Greek Lexicon
ἅπαξ, adv., once, one time, [fr. ΠΣ; down]; a. univ.: 2 Co. xi. 25; Heb. ix. 26 sq.; 1 Pet. iii. 20 Rec.; ἔτι ἅπαξ, Heb. xii. 26 sq. ; ἅπαξ τοῦ ἐνιαυτοῦ, Heb. ix. 7, [Hat. 2, 59, ete.]. Ὁ. like Lat. semel, used of what is so done as to be of perpetual validity and never need repetition, once for all: Heb.vi.4; x.2; 1 Pet. iii. 18; Jude vss. 3, 5. 6. καὶ ἅπαξ καὶ δίς indicates a definite number [the double καί emphasizing the repetition, both once and again i. 6.1 twice: 1 Th.ii.18; Phil. iv. 16; on the other hand, ἅπαξ καὶ δίς means [once and again i. e.] several times, repeatedly: Neh. xiii. 20; 1 Mace. iii. 30. Cf. Schott on 1 Th. ii. 18, p. 86; [Meyer on Phil. 1. c.].
Mounce Concise Greek Dictionary
ἅπαξ hapax 14x
once, 2 Cor. 11:25; once for all, Heb. 6:4; 9:26, 28; 10:2; 1 Pet. 3:18, 20; Jude 3; εἰδὼς ἅπαξ, knowing once for ever, unfailingly, constantly, Jude 5
Abbott-Smith Greek Lexicon
ἅπαξ, adv.,
[in LXX for אֶחָד, פַּעַם;]
once: II Co 11:25, He 9:26, 27; ἔτι ἅ., He 12:26, 27; ἅ. τ. ἐνιαυτοῦ, He 9:7; καί ἅ. κ. δίς, twice: Phl 4:16, I Th 2:18;
once for all: He 6:4 9:28 10:2, I Pe 3:18, Ju 3, 5 (MM, VGT, s.v.).†
Liddell-Scott-Jones — Greek-English Lexicon
ἅπαξ (hapax) — once. ἅπαξ [ᾰπ], adverb once, once only, once for all, first in [Refs 8th c.BC+]; ἅ... ἀπὸ θυμὸν ὀλέσσαι[Refs 5th c.BC+]; οὐχ ἅ. μόνον more than once, [Refs 5th c.BC+]; of the self-creation of Νοῦς, τὴν ποίησιν αὑτοῦ.. ἅ. εἶναι[Refs 3rd c.AD+]; ἅ. ἔτι yet this once, [Refs 4th c.BC+]; τὸ ἅ. τοῦτο at this moment, [LXX]; ἅ. δυοῖν ποδοῖν, i.e. two square feet [Refs]four, [Refs 5th c.BC+]
2. with genitive, ἅ. τοῦ ἐνιαυτοῦ, ἔτεος ἑκάστου ἅ., [Refs 5th c.BC+]
3. once on a time, formerly, ἅ. καὶ ἅ.[LXX]
II. without any notion of number, after conditional and temporal Particles, if once, when once, εἴπερ ἐσπείσω γ᾽ ἅ. if once you have made a treaty, [Refs 5th c.BC+]: so with participle, ἐπὶ γᾶν ἅ. πεσὸν... αἷμα[NT+5th c.BC+] = sṃ (compare εἷς); -παξ akin to πήγνυμι.)