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

Category: Animals

2.Definition: a small sharp-pointed tip resembling a spike on a stem or leaf

Related Noun(s):pricker, prickle, spikelet, sticker, thorn

Category: Plants

3.Definition: any sharply pointed projection

Related Noun(s):acantha, spur

Category: General

4.Definition: 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"

Related Noun(s):backbone

Category: Objects

5.Definition: the series of vertebrae forming the axis of the skeleton and protecting the spinal cord

Related Noun(s):back, backbone, rachis

Category: General