What is the meaning of spine?

noun

• The series of vertebrae forming the axis of the skeleton and protecting the spinal cord.
  • usage: "the fall broke his back"
  • synonyms: spinal column, vertebral column, backbone, back, rachis
• Any sharply pointed projection.
  • synonyms: spur, acantha
• A small sharp-pointed tip resembling a spike on a stem or leaf.
  • synonyms: thorn, prickle, pricker, sticker, spikelet
• 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.
  • usage: "the title and author were printed on the spine of the book"
  • synonyms: backbone
• A sharp rigid animal process or appendage; as a porcupine quill or a ridge on a bone or a ray of a fish fin. .