1.1. In English Dictionaries and Encyclopedias

• apostle | Merriam-Webster’s collegiate dictionary. (Eleventh ed.)

1.2. In Bible Dictionaries and Encyclopedias

• Apostle, Apostleship. | Baker Encyclopedia of the Bible
• Authority, Human | Dictionary of Biblical Imagery
• Apostle | Dictionary of Jesus and the Gospels
• Apostle, Apostleship | Dictionary of the later New Testament and its developments
• Apostle | Dictionary of Paul and his letters

1.3. In Theological Dictionaries and Encyclopedias

1.4. In Theological Journals

2.1. In Systematic Theologies

2.2. In Other Books