Quick Definition
ἀθέτησις, εως, ἡ n.f. nullification, abrogation
Strong's Definition
from 114; cancellation (literally or figuratively)
KJV Usage: disannulling, put away
UBS Dictionary of the Greek New Testament
UBS Dictionary of the Greek New Testament © United Bible Societies, licensed CC BY-SA 4.0.
Thayer's Greek Lexicon
ἀθέτησις, -ews, ἡ, (ἀθετέω, q. νι; like νουθέτησις fr. νουθετεῖν), abolition: Heb. vii. 18; ix. 26; (found occasionally in later authors, as Cicero ad Att. 6, 9; Diog. Laért. 3, 39, 66; in the grammarians rejection; more frequently in eccl. writ.).
Mounce Concise Greek Dictionary
ἀθέτησις athetēsis 2x
abrogation, annulling, Heb. 7:18; 9:26*
Abbott-Smith Greek Lexicon
† ἀθέτησις, -εως, ἡ
(< ἀθετέω), [in LXX, usually of unfaithful, rebellious action: I Ki 24:12 (פֶּשַׁע), Je 12:1 (בֶּגֶד), Da TH 9:7 (מַעַל), II Mac 14:28*;]
a disannulling, setting aside: He 7:18 9:26 (for similar usage in π., v. Deiss., BS, 228 f.; MM, VGT, s.v.).†
Moulton & Milligan — Vocabulary of the Greek NT
ἀθέτησις. The force of ἀθέτησις in Heb γ15, 9° is well brought out by Deissmann’s reference (4S p. 228 f.) to the technical legal formula in the papyri els ἀθέτησιν καὶ ἀκύρωσιν, as in BGU I. 4415 (A.D. 102) τὴν δίια)γραφὴν els ἀθέτησιν καὶ | ἀκύρωσιν, ‘the decree to be annulled and cancelled.” So
Liddell-Scott-Jones — Greek-English Lexicon
ἀθέτησις (athetēsis) — nullification. ἀθέτ-ησις, ἡ, a setting aside, abolition, ἁμαρτίας[NT+2nd c.AD+]; 'annulling' of a deed, [Refs 1st c.AD+]
II. rejection (of a spurious passage), [Refs 2nd c.AD+]; generally, rejection, opposed to ἐποχή, [Refs 1st c.BC+]
III. breach of faith, [Refs 2nd c.AD+]