σύνδουλος

a fellow servant, one who serves the same master with another, the associate of a servant (or slave), one who with others serves (ministers to) a king, a colleague of one who is Christ's servant in publishing the gospel, one who with others acknowledges the same Lord, Jesus, and obeys his commands, one who with others is subject to the same divine authority in the Messianic economy, of angels as the fellow servants of Christians