The Greek aptaistos means without stumbling, faultlessly, or in a way that does not falter or fail. It combines a (negative) with ptaió (to stumble, to trip).
Aptaistos appears once in the New Testament in Jude 24 — one of the most beloved doxologies in Scripture: 'To him who is able to keep you from stumbling (aptaistos) and to present you before his glorious presence without fault and with great joy.' The word captures the ultimate promise of the Christian life: God's preserving grace that carries believers through every trial to a final, faultless presentation before His throne. What humans cannot achieve through effort, God accomplishes through His power. The doxology grounds security not in human performance but in divine ability.