A "publisher of glad tidings;" a missionary preacher of the gospel (Ephesians 4:11). This title is applied to Philip (Acts 21:8), who appears to have gone from city to city preaching the word (8:4, 40). Judging from the case of Philip, evangelists had neither the authority of an apostle, nor the gift of prophecy, nor the responsibility of pastoral supervision over a portion of the flock. They were itinerant preachers, having it as their special function to carry the gospel to places where it was previously unknown. The writers of the four Gospels are known as the Evangelists.

Noah Webster's New International Dictionary of the English Language

(n.) A missionary preacher; a bringer of the good news. Specially: (a) A missionary preacher sent forth to prepare the way for a resident pastor; an itinerant missionary preacher. (b) A writer of one of the four Gospels (With the definite article); as, the four evangelists, Matthew, Mark, Luke, and John. (c) A traveling preacher whose efforts are chiefly directed to arouse to immediate repentance.