Originally the trigger-stick of a trap that snaps shut when touched, skandalon came to mean anything that causes someone to stumble, fall into sin, or lose faith. The English 'scandal' derives from it but has lost the biblical sharpness: a skandalon is not merely embarrassing but spiritually lethal.
Paul declares the cross to be a skandalon to Jews (1 Cor 1:23) — a crucified Messiah was a stumbling block to anyone expecting a conquering king. Peter becomes a skandalon to Jesus when he opposes the cross (Matt 16:23). Romans 14:13 turns it into an ethical principle: 'never put a skandalon or stumbling block in your brother's way.' The word forces a choice: the cross is either the power of God unto salvation or the great offense — there is no neutral ground.