The Collaborative International Dictionary of English v.0.48:

evangelist \e*van"gel*ist\ ([-e]*v[a^]n"j[e^]l*[i^]st), n. [F.
   ['e]vang['e]liste, L. evangelista, fr. Gr. e'yaggelisth`s.]
   A bringer of the glad tidings of Church and his doctrines.
   Specifically:
   (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.
       [1913 Webster]

             The Apostles, so far as they evangelized, might
             claim the title though there were many evangelists
             who were not Apostles.               --Plumptre.
       [1913 Webster]

WordNet (r) 3.0 (2006):

evangelist
    n 1: a preacher of the Christian gospel [syn: evangelist,
         revivalist, gospeler, gospeller]
    2: (when capitalized) any of the spiritual leaders who are
       assumed to be authors of the Gospels in the New Testament:
       Matthew, Mark, Luke, and John

The Devil's Dictionary (1881-1906):

EVANGELIST, n.  A bearer of good tidings, particularly (in a religious
sense) such as assure us of our own salvation and the damnation of
our neighbors.