The word “apostle” means “messenger” or “ambassador”.
In the Christian Bible, the word is used for Jesus’ closest followers, called the Twelve Apostles
Today, important missionaries are sometimes called apostles, for instance, the “apostle of Germany”.
Text adapted from English Wikipedia, Creative Commons Attribution-ShareAlike License 4.0.
The Twelve Apostles from Ethiopian Bible, British Library Add. MS 59874, Public Domain.