spine

noun

1. the series of vertebrae forming the axis of the skeleton and protecting the spinal cord"the fall broke his back"
2. any sharply pointed projection
3. a small sharp-pointed tip resembling a spike on a stem or leaf
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"
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