The Collaborative International Dictionary of English v.0.48:

Commonplace \Com"mon*place`\, n.
   1. An idea or expression wanting originality or interest; a
      trite or customary remark; a platitude.
      [1913 Webster]

   2. A memorandum; something to be frequently consulted or
      referred to.
      [1913 Webster]

            Whatever, in my reading, occurs concerning this our
            fellow creature, I do never fail to set it down by
            way of commonplace.                   --Swift.
      [1913 Webster]

   Commonplace book, a book in which records are made of
      things to be remembered.
      [1913 Webster]

WordNet (r) 3.0 (2006):

commonplace book
    n 1: a notebook in which you enter memorabilia