sacrum

• POS: Noun
• HYPHEN: sac=rum

CIDE DICTIONARY

sacrum, n. [NL., fr. L. sacer sacred, os sacrum the lowest bone of the spine.].

 That part of the vertebral column which is directly connected with, or forms a part of, the pelvis.  [1913 Webster]
" 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 vertebræ, which diminish in size very rapidly to the posterior extremity, which bears the coccyx."  [1913 Webster]

OXFORD DICTIONARY

sacrum, n. (pl. sacra or sacrums) Anat. a triangular bone formed from fused vertebrae and situated between the two hip-bones of the pelvis.

Etymology

L os sacrum transl. Gk hieron osteon sacred bone (from its sacrificial use)