sacrum

 
Pronunciation: /ˈseɪkrəm, ˈsak-/

noun (plural sacra /-krə/ or sacrums)

Anatomy
  • a triangular bone in the lower back formed from fused vertebrae and situated between the two hip bones of the pelvis.

Origin:

mid 18th century: from Latin os sacrum, translation of Greek hieron osteon 'sacred bone' (from the belief that the soul resides in it)