backbone

noun

Etymology: From Middle English bakbon, bakebon, bac-bon; equivalent to back + bone. Compare the semantically analogous English ridgebone.

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. Any fundamental support, structure, or infrastructure.

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

   “Undoubtedly it can be said that the humble 0-6-0 has been the backbone for general service, or general utility on British railways right from their earliest days, and is likely to remain so.”

3. Courage, fortitude, or strength.

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

   “His appearance was certainly that of a hairdresser's dummy; but in the great demoralization of the land he kept up his appearance. That's backbone. His starched collars and got-up shirt-fronts were achievements of character. He had been out nearly three years; and, later, I could not help asking him how he managed to sport such linen.”