This rare compound appears only in Peter's closing greeting, where the church 'in Babylon' is called 'co-chosen' with the recipients. The prefix συν- ('together') intensifies the theological weight: not merely chosen, but chosen alongside them in God's electing purposes. Translations across languages preserve the participatory sense—German 'miterwählte,' Spanish 'co-elegida'—highlighting the shared election of communities scattered across the empire.