vertebra

n. segments of bone which form the spinal column

The Vertebral Column (singular: vertebra) are the individual irregular bones that make up the spinal column (aka ischis) — a flexuous and flexible column. There are normally thirty-three (33) vertebrae in humans, including the five that are fused to form the sacrum (the others are separated by intervertebral discs) and the four coccygeal bones which form the tailbone. The upper three regions comprise the remaining 24, and are grouped under the names cervical (7 vertebrae), thoracic (12 vertebrae) and lumbar (5 vertebrae), according to the regions they occupy. This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another. The number of cervical vertebrae is, however, very rarely increased or diminished.
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Vertebra /ver·te·bra/ pl. ver´tebrae [L.] any of the 33 bones of the vertebral column, comprising 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and [more]Vertebra - Community and Resources

Noun
1. one of the bony segments of the spinal column
(hypernym) bone, os
(hyponym) cervical vertebra, neck bone
(part-holonym) spinal column, vertebral column, spine, backbone, back, rachis
(part-meronym) centrum

n. vertebra, segments of bone which form the spinal column