noun

1. any of the stiff, sharp-pointed, superficial emergences on a plant, as on a rose, thistle, or cactus
2. 1. a sharp process of bone
   2. any of the sharp, stiff projections on the bodies of certain animals, as the quill of a porcupine or a ray of a fish's fin
   3. anything resembling either of these projections
3. the spinal column; backbone
4. anything regarded as resembling a backbone, as
   1. a ridge of ground, crest of a hill, etc.
   2. the part of a bound book covering the backbone, and usually bearing the title and author's name
5. ☆ courage, willpower, etc.

Etymology: ME < OFr espine < L spina, thorn, prickle, backbone: see spike