The Collaborative International Dictionary of English v.0.48:

Teacher \Teach"er\, n.
   1. One who teaches or instructs; one whose business or
      occupation is to instruct others; an instructor; a tutor.
      [1913 Webster]

   2. One who instructs others in religion; a preacher; a
      minister of the gospel; sometimes, one who preaches
      without regular ordination.
      [1913 Webster]

            The teachers in all the churches assembled. --Sir W.
                                                  Raleigh.
      [1913 Webster]

WordNet (r) 3.0 (2006):

teacher
    n 1: a person whose occupation is teaching [syn: teacher,
         instructor]
    2: a personified abstraction that teaches; "books were his
       teachers"; "experience is a demanding teacher"