The Collaborative International Dictionary of English v.0.48:

Spine \Spine\, n. [L. spina thorn, the spine; akin to spica a
   point: cf. OF. espine, F. ['e]pine. Cf. Spike, Spinet a
   musical instrument, Spinny.]
   1. (Bot.) A sharp appendage to any of a plant; a thorn.
      [1913 Webster]

   2. (Zool.)
      (a) A rigid and sharp projection upon any part of an
          animal.
      (b) One of the rigid and undivided fin rays of a fish.
          [1913 Webster]

   3. (Anat.) The backbone, or spinal column, of an animal; --
      so called from the projecting processes upon the
      vertebrae.
      [1913 Webster]

   4. Anything resembling the spine or backbone; a ridge.
      [1913 Webster]

WordNet (r) 3.0 (2006):

spine
    n 1: the series of vertebrae forming the axis of the skeleton
         and protecting the spinal cord; "the fall broke his back"
         [syn: spinal column, vertebral column, spine,
         backbone, back, rachis]
    2: any sharply pointed projection [syn: spur, spine,
       acantha]
    3: a small sharp-pointed tip resembling a spike on a stem or
       leaf [syn: spine, thorn, prickle, pricker, sticker,
       spikelet]
    4: the part of a book's cover that encloses the inner side of
       the book's pages and that faces outward when the book is
       shelved; "the title and author were printed on the spine of
       the book" [syn: spine, backbone]
    5: a sharp rigid animal process or appendage; as a porcupine
       quill or a ridge on a bone or a ray of a fish fin