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1. The vertebrate spine or spinal column.
2. Something, such as the keel of a ship, that resembles a backbone.
3. The main support or major sustaining factor: the backbone of a thesis.
4. Strength of character; determination: displayed grit and backbone in facing adversity.
a. A ridge forming the principal axis of a mountain.
b. The principal mountain ridge, range, or system of a region.
6. Chemistry The main chain of atoms in a polymer.
7. Computers A high-speed communications line that connects smaller, local networks to each other, especially in a wide area network.