G0646
ἀποστασία
apostasy
άποστασία, -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, frequently in sense of political revolt, in LXX (e.g. Jos.22:22, 2Ch.29:19, Jer.2:19) and NT always of religious apostasy: Act.21:21, 2Th.2:3.† (AS)
Full Thayer's lexicon entry
ἀποστασία — apostasía
ἀποστασία, ἀποστασιας, ἡ (ἀφισταμαι), a falling away, defection, apostasy; in the Bible namely, from the true religion: Act 21:21; 2Th 2:3; ((Jos 22:22; 2Ch 29:19; 2Ch 33:19); Jer 2:19; Jer 36:1-32 :(29) 32 Complutensian; 1Ma 2:15). The earlier Greeks say ἀπόστασις; see Lob. ad Phryn., p. 528; (Winer's Grammar, 24).
2 occurrences
Acts (1), II Thessalonians (1)