backbone

noun

1. 1

   The series of vertebrae, separated by disks, that encloses and protects the spinal cord, and runs down the middle of the back in vertebrate animals.

2. 2

   Any fundamental support, structure, or infrastructure.

   “Before automobiles, railroads were a backbone of commerce.”

3. 3

   Courage, fortitude, or strength.

   “He would make a good manager, if he had a little more backbone.”