The Collaborative International Dictionary of English v.0.48:

Preacher \Preach"er\ (pr[=e]ch"[~e]r), n. [Cf. OF. preeschierre,
   prescheur, F. pr[^e]cheur, L. praedicator.]
   1. One who preaches; one who discourses publicly on religious
      subjects.
      [1913 Webster]

            How shall they hear without a preacher? --Rom. x.
                                                  14.
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   2. One who inculcates anything with earnestness.
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            No preacher is listened to but Time.  --Swift.
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   Preacher bird (Zool.), a toucan.
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WordNet (r) 3.0 (2006):

preacher
    n 1: someone whose occupation is preaching the gospel [syn:
         preacher, preacher man, sermonizer, sermoniser]