spine

the series of vertebrae forming the axis of the skeleton and protecting the spinal cord; "the fall broke his back"

any sharply pointed projection

a small sharp-pointed tip resembling a spike on a stem or leaf

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"

a sharp rigid animal process or appendage; as a porcupine quill or a ridge on a bone or a ray of a fish fin