Lexical Definition

‎ἅπαξ‎ hápax (hap'-ax) once G:ADV
probably from ‎ἅπας‎

once.

Usage: 2 forms in 44 verses

Abbott-Smith

ἅπαξ, adv., [in LXX for אֶחָד, פַּעַם;]
(a) 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;
(b) once for all: He 6:4 9:28 10:2, I Pe 3:18, Ju 3, 5 (MM, VGT, s.v.).†

Abbott-Smith References

Book Refs
2 Corinthians 11:25
Philippians 4:16
1 Thessalonians 2:18
Hebrews 6:4 · 9:7 · 9:26 · 9:27 · 9:28 · 10:2 · 12:26 · 12:27
1 Peter 3:18
Jude 1:3 · 1:5

Liddell-Scott-Jones

ἅπαξ [ᾰπ],

adverb once, once only, once for all, first in [Refs 8th c.BC+]; ... ἀπὸ θυμὸν ὀλέσσαι[Refs 5th c.BC+]; οὐχ . μόνον more than once, [Refs 5th c.BC+]; of the self-creation of Νοῦς, τὴν ποίησιν αὑτοῦ.. . εἶναι[Refs 3rd c.AD+]; . ἔτι yet this once, [Refs 4th c.BC+]; τὸ . τοῦτο at this moment, [LXX]; . δυοῖν ποδοῖν, i.e. two square feet [Refs]four, [Refs 5th c.BC+]

__2 with genitive, . τοῦ ἐνιαυτοῦ, ἔτεος ἑκάστου ., [Refs 5th c.BC+]
__3 once on a time, formerly, . καὶ .[LXX]
__II without any notion of number, after conditional and temporal Particles, if once, when once, εἴπερ ἐσπείσω γ᾽ . if once you have made a treaty, [Refs 5th c.BC+]: so with participle, ἐπὶ γᾶν . πεσὸν... αἷμα[NT+5th c.BC+] = sṃ (compare εἷς); -παξ akin to πήγνυμι.)

LSJ Scripture Refs: LXX.2Kgs.17.7LXX.Judg.20.30Heb.6.4