G0679
ἄπταιστος
without falling
ἄ-πταιστος, -ον (πταίω), [in LXX: 3Ma.6:39 * ;] without stumbling, sure-footed: metaphorically (MM, see word), Ju 24.† (AS)
Full Thayer's lexicon entry
ἄπταιστος — áptaistos
ἄπταιστος, ἀπτιαστον (πταίω, which see), not stumbling, standing firm, exempt from falling (properly, of a horse, Xenophon, de re eq. 1, 6); metaphorically: Jud 1:24. (Cf. Winers Grammar, 97 (92); Buttmann, 42 (37).)
1 occurrence