1. a central cohesive source of support and stability

Similar word(s): anchor, keystone, linchpin, lynchpin, mainstay

Definition categories: thought, support

2. fortitude and determination

Similar word(s): grit, gumption, guts, moxie, sand

Definition categories: attribute, fortitude

3. the series of vertebrae forming the axis of the skeleton and protecting the spinal cord

- the fall broke his back

Similar word(s): back, rachis, spine

Definition categories: body

4. 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

Similar word(s): spine

Definition categories: man–made, part, portion

5. the part of a network that connects other networks together

- the backbone is the part of a communication network that carries the heaviest traffic

Definition categories: man–made, connecter, connection, connective, connector, connexion

Sentences with backbone as a noun:

- Before automobiles, railroads were a backbone of commerce.

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