A Greek preposition meaning with, together with, in company with, in association with. It denotes close accompaniment, joint participation, and intimate association. In compound verbs (syn- prefix), it intensifies the idea of doing something together: syn-ergos (co-worker), syn-pathein (to suffer with), syn-zōopoieō (to make alive together).
Paul's 'syn-' compounds form the backbone of his union-with-Christ theology. Believers have been crucified with Christ (syn-stauroō, Galatians 2:20), buried with Him (syn-thaptō, Romans 6:4), raised with Him (syn-egeirō, Colossians 3:1), made alive with Him (syn-zōopoieō, Ephesians 2:5), and will be glorified with Him (syn-doxazō, Romans 8:17). This little preposition carries the weight of the gospel: everything Christ experienced, believers experience in Him. We don't merely benefit from Christ's work; we are united with Him in it. The Christian life is not imitation of Christ from a distance, but participation with Christ in His death and resurrection.