backbone

(noun) a central cohesive source of support and stability. Synonyms: anchor, mainstay, keystone, linchpin, lynchpin. Examples: "Faith is his anchor." "The keystone of campaign reform was the ban on soft money." "He is the linchpin of this firm."

(noun) fortitude and determination. Synonyms: grit, guts, moxie, sand, gumption. Examples: "He didn't have the guts to try it."

(noun) the series of vertebrae forming the axis of the skeleton and protecting the spinal cord. Synonyms: spinal column, vertebral column, spine, back, rachis. Examples: "The fall broke his back."

(noun) 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. Synonyms: spine. Examples: "The title and author were printed on the spine of the book."

(noun) the part of a network that connects other networks together. Examples: "The backbone is the part of a communication network that carries the heaviest traffic."