backbonen.[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.()