'Sacrum' definitions:

Definition of 'sacrum'

(from WordNet)
noun
Wedge-shaped bone consisting of five fused vertebrae forming the posterior part of the pelvis; its base connects with the lowest lumbar vertebra and its tip with the coccyx

Definition of 'Sacrum'

From: GCIDE
  • Sacrum \Sa"crum\, n.; pl. sacra. [NL., fr. L. sacer sacred, os sacrum the lowest bone of the spine.] (Anat.) That part of the vertebral column which is directly connected with, or forms a part of, the pelvis. [1913 Webster]
  • Note: It may consist of a single vertebra or of several more or less consolidated. In man it forms the dorsal, or posterior, wall of the pelvis, and consists of five united vertebrae, which diminish in size very rapidly to the posterior extremity, which bears the coccyx. [1913 Webster]