Source : Webster's Revised Unabridged Dictionary (1913)

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

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

            The teachers in all the churches assembled. --Sir W.
                                                  Raleigh.

Source : WordNet®

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