n.1. The spinal column of a vertebrate.
2. Zoology Any of various pointed projections, processes, or appendages of animals.
3. Botany a. A strong, sharp-pointed outgrowth derived from a leaf or leaf part.
b. Any of various similar sharp structures, such as a thorn.
4. Something that resembles or suggests a backbone, as:
a. The hinged back of a book.
b. The crest of a ridge.
5. Strength of character; courage or willpower.