The Collaborative International Dictionary of English v.0.48:

Bookworm \Book"worm`\, n.
   1. (Zool.) Any larva of a beetle or moth, which is injurious
      to books. Many species are known.
      [1913 Webster]

   2. A student closely attached to books or addicted to study;
      a reader without appreciation.
      [1913 Webster]

            I wanted but a black gown and a salary to be as mere
            a bookworm as any there.              --Pope.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bookworm
    n 1: a person who pays more attention to formal rules and book
         learning than they merit [syn: pedant, bookworm,
         scholastic]
    2: someone who spends a great deal of time reading