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

Moby Thesaurus II by Grady Ward, 1.0:

155 Moby Thesaurus words for "spine":
   advocate, alpenstock, arm, athletic supporter, back, backbone,
   backing, bandeau, barb, barbel, barbule, bearer, bilge, blain,
   bleb, blister, blob, boss, bow, bra, brace, bracer, bracket,
   bramble, brassiere, brier, bristle, bubble, bulb, bulge, bulla,
   bump, bunch, burl, burr, button, buttress, cactus, cahot, cane,
   carrier, catchweed, cervix, chine, cleavers, clump, col, comb,
   condyle, convex, corset, crook, crutch, dowel, ear, esker, flange,
   flap, foundation garment, fulcrum, gall, girdle, gnarl,
   goose grass, guy, guywire, handle, hill, hogback, horseback, hump,
   hunch, jock, jockstrap, jog, joggle, kame, knob, knot, knur, knurl,
   lip, loop, lump, mainstay, maintainer, mast, mole, mountain, neck,
   needle, nettle, nevus, nub, nubbin, nubble, papilloma, peg,
   pine needle, prickle, prong, prop, quill, rachis, ray, reinforce,
   reinforcement, reinforcer, rest, resting place, rib, ridge,
   rigging, ring, saddle, saddleback, shoulder, shroud, spicula,
   spicule, spiculum, spike, spikelet, spinal column, spinal cord,
   sprit, spur, staff, standing rigging, stave, stay, stick, sticker,
   stiffener, strengthener, stud, style, support, supporter,
   sustainer, tab, thistle, thorn, tubercle, tubercule, upholder,
   verruca, vertebrae, vertebral column, vesicle, wale, walking stick,
   wart, welt, yucca