The Collaborative International Dictionary of English v.0.48:

Codex \Co"dex\ (k[=o]"d[e^]ks), n.; pl. Codices. [L. See
   Code.]
   1. A book, especially an early form of book with pages
      stitched together, contrasting with the earlier scrolls; a
      manuscript; as, a DaVinci codex.
      [1913 Webster]

   2. A collection or digest of laws; a code(senses 2 or 4).
      [archaic] --Burrill.
      [1913 Webster]

   3. An ancient manuscript of the Sacred Scriptures, or any
      part of them, particularly the New Testament.
      [1913 Webster]

   4. A collection of canons. --Shipley.
      [1913 Webster]

WordNet (r) 3.0 (2006):

codex
    n 1: an official list of chemicals or medicines etc.
    2: an unbound manuscript of some ancient classic (as
       distinguished from a scroll) [syn: codex, leaf-book]