Backbone \Back"bone"\, n. [2d back,n.+ bone. ]

1. The column of bones in the back which sustains and gives firmness to the frame; the spine; the vertebral or spinal column.

2. Anything like, or serving the purpose of, a backbone.

The lofty mountains on the north side compose the granitic axis, or backbone of the country. --Darwin.

We have now come to the backbone of our subject. --Earle.

3. Firmness; moral principle; steadfastness.

Shelley's thought never had any backbone. --Shairp.

To the backbone, through and through; thoroughly; entirely. ``Staunch to the backbone.'' --Lord Lytton.

Source: Webster's Revised Unabridged Dictionary (1913)