Noun

1. The series of vertebrae forming the axis of the skeleton and protecting the spinal cord
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
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