"Because the way of Jesus to the cross became a σκάνδαλον* to Peter, he himself became σκάνδαλον to Jesus, i.e., a personified temptation to turn aside from God's will."
~Kittel, Gerhard, Gerhard Friedrich, eds. Theological Dictionary of the New Testament, vol. 7 (Grand Rapids: Eerdmans, 1964-1976), 348.
*Gk., a stone that trips someone or springs a trap to ensnare them