An apostle (/əˈpɒsəl/), in its most literal sense, is an emissary, from Greek ἀπόστολος (apóstolos), literally "one who is sent off", from the verb ἀποστέλλειν (apostéllein), "to send off". The purpose of such sending off is usually to convey a message, and thus "messenger" is a common alternative translation; other common translations include "ambassador" and "envoy".
The term derives from the Greek of the New Testament and was used for Jesus's original Twelve Apostles (including Peter, James, and John), as well as a wider group of early Christian figures, including Paul, Barnabas, and Junia. Some other religions use the term for comparable figures in their history. The word in this sense may be used metaphorically in various contexts, but is mostly found used specifically for early associates of the founder of a religion, who were important in spreading his or her teachings.
The adjective apostolic (/ˌæpəˈstɒlɪk/) is claimed as a continuing characteristic by a number of prominent Christian churches (i.e., that a given church's traditions, practices, and teachings descend directly from the original apostles), and so finds wider modern application. The word is found, for example, in the "Apostolic See", the official name for the Roman Catholic Papacy; in the doctrine of apostolic succession, held by many branches of Christianity; and in the Four Marks of the Church ("one, holy, catholic, and apostolic") found in the Nicene-Constantinopolitan Creed.