The Collaborative International Dictionary of English v.0.48:

Reader \Read"er\ (r[=e]d"[~e]r), n. [AS. r[=ae]dere.]
   1. One who reads. Specifically:
      (a) One whose distinctive office is to read prayers in a
          church.
      (b) (University of Oxford, Eng.) One who reads lectures on
          scientific subjects. --Lyell.
      (c) A proof reader.
      (d) One who reads manuscripts offered for publication and
          advises regarding their merit.
          [1913 Webster]

   2. One who reads much; one who is studious.
      [1913 Webster]

   3. A book containing a selection of extracts for exercises in
      reading; an elementary book for practice in a language; a
      reading book.
      [1913 Webster]

WordNet (r) 3.0 (2006):

reader
    n 1: a person who enjoys reading
    2: someone who contracts to receive and pay for a service or a
       certain number of issues of a publication [syn: subscriber,
       reader]
    3: a person who can read; a literate person
    4: someone who reads manuscripts and judges their suitability
       for publication [syn: reviewer, referee, reader]
    5: someone who reads proof in order to find errors and mark
       corrections [syn: proofreader, reader]
    6: someone who reads the lessons in a church service; someone
       ordained in a minor order of the Roman Catholic Church [syn:
       lector, reader]
    7: a public lecturer at certain universities [syn: lector,
       lecturer, reader]
    8: one of a series of texts for students learning to read