Source : Webster's Revised Unabridged Dictionary (1913)

Vertebra \Ver"te*bra\, n.; pl. {Vertebr[ae]}. [L. vertebra, fr.
   vertere to turn, change. See {Verse}.]
   1. (Anat.) One of the serial segments of the spinal column.

   Note: In many fishes the vertebr[ae] are simple cartilaginous
         disks or short cylinders, but in the higher vertebrates
         they are composed of many parts, and the vertebr[ae] in
         different portions of the same column vary very
         greatly. A well-developed vertebra usually consists of
         a more or less cylindrical and solid body, or centrum,
         which is surmounted dorsally by an arch, leaving an
         opening which forms a part of the canal containing the
         spinal cord. From this dorsal, or neural, arch spring
         various processes, or apophyses, which have received
         special names: a dorsal, or neural, spine, spinous
         process, or neurapophysis, on the middle of the arch;
         two anterior and two posterior articular processes, or
         zygapophyses; and one or two transverse processes on
         each side. In those vertebr[ae] which bear
         well-developed ribs, a tubercle near the end of the rib
         articulates at a tubercular facet on the transverse
         process (diapophysis), while the end, or head, of the
         rib articulates at a more ventral capitular facet which
         is sometimes developed into a second, or ventral,
         transverse process (parapophysis). In vertebrates with
         well-developed hind limbs, the spinal column is divided
         into five regions in each of which the vertebr[ae] are
         specially designated: those vertebr[ae] in front of, or
         anterior to, the first vertebra which bears ribs
         connected with the sternum are cervical; all those
         which bear ribs and are back of the cervicals are
         dorsal; the one or more directly supporting the pelvis
         are sacral and form the sacrum; those between the
         sacral and dorsal are lumbar; and all those back of the
         sacral are caudal, or coccygeal. In man there are seven
         cervical vertebr[ae], twelve dorsal, five lumbar, five
         sacral, and usually four, but sometimes five and rarely
         three, coccygeal.

   2. (Zo["o]l.) One of the central ossicles in each joint of
      the arms of an ophiuran.

Source : WordNet®

vertebra
     n : one of the bony segments of the spinal column
     [also: {vertebrae} (pl)]

vertebrae
     See {vertebra}