Lexical Definition

‎ἀποστασία‎ apostasía (ap-os-tas-ee'-ah) apostasy ^G:N-F
feminine of the same as ‎ἀποστάσιον‎

falling away, forsake.

• defection from truth (properly, the state) ("apostasy")

Abbott-Smith

† ἀποστασία, -ας, ἡ (< ἀφίστημι), [in LXX for מַעַל, etc.;]
defection, apostasy, revolt; in late Gk. (MM, Exp., viii; Lft., Notes, 111; Cremer, 308) for cl. ἀπόστασις, freq. in sense of political revolt, in LXX (e.g. Jos 22:22, II Ch 29:19, Je 2:19) and NT always of religious apostasy: Ac 21:21, II Th 2:3.†

Abbott-Smith References

Liddell-Scott-Jones

ἀποστασία-στᾰσία, ἡ,

late form for ἀπόστασις, defection, revolt, variant in [Refs 1st c.BC+]; especially in religious sense, rebellion against God, apostasy, [LXX+NT]

__2 departure, disappearance, [Refs 6th c.AD+]
__3 distinguishing, with genitive, [Refs 6th c.AD+]
__4 distance, [Refs 3rd c.BC+]

_{LSJ Scripture Refs: LXX.Josh.22.22 ☩ 2Thess.2.3}