Definition of "Spine" :
noun: a sharp rigid animal process or appendage; as a porcupine quill or a ridge on a bone or a ray of a fish fin
noun: 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."
noun: the series of vertebrae forming the axis of the skeleton and protecting the spinal cord
noun: a small sharp-pointed tip resembling a spike on a stem or leaf
noun: any sharply pointed projection