backbone (spinal column, spine, vertebral column) (bak-bohn) n. the flexible bony column, extending from the base of the skull to the small of the back, that encloses and protects the spinal cord. It is made up of individual bones (see vertebra) connected by discs of fibrocartilage (see intervertebral disc). The backbone of a newborn baby contains 33 vertebrae: seven cervical, 12 thoracic, five lumbar, five sacral, and four coccygeal. In the adult the sacral and coccygeal vertebrae become fused into two single bones (sacrum and coccyx, respectively). See illustration. Anatomical name: rachis.

back·bone / ˈbakˌbōn/ • n. the series of vertebrae extending from the skull to the pelvis; the spine. ∎ fig. the chief support of a system or organization; the mainstay: these firms are the backbone of our industrial sector. ∎ fig. strength of character; firmness: he has the backbone to see us through this difficulty.

backbone See vertebral column.