The Greek noun apostole means apostleship, a commission, or the office/mission of being sent. It is the abstract noun from apostolos (apostle), referring to the divine sending and the authoritative office of an apostle. The word captures not just the role but the divine mandate behind it.
Apostole emphasizes the authority and divine commissioning behind the apostolic office. When Paul defends his ministry, he consistently appeals to his apostleship (apostole) as something received directly from God, not from men (Galatians 1:1). The office of apostle was foundational to the early church — apostles were eyewitnesses of the risen Christ, entrusted with the authoritative transmission of the gospel. The church is 'built on the foundation of the apostles and prophets, with Christ Jesus himself as the chief cornerstone' (Ephesians 2:20). Apostole thus names the divine missionary commission that planted and established the church.