Source : Webster's Revised Unabridged Dictionary (1913)

Centrum \Cen"trum\, n.; pl. E. {Centrums}, L. {Centra}. [L.,
   center.] (Anat.)
   The body, or axis, of a vertebra. See {Vertebra}.

Source : WordNet®

centrum
     n : the main body of a vertebra
     [also: {centra} (pl)]