sacrum
noun /ˈseɪkrəm/,  /ˈsækrəm/
  /ˈseɪkrəm/,  /ˈsækrəm/
 (plural sacra 
 (anatomy) /ˈseɪkrə/,  /ˈsækrə/
  /ˈseɪkrə/,  /ˈsækrə/
, sacrums)- a bone in the lower back, between the two hip bones of the pelvisTopics Bodyc2Word Originmid 18th cent.: from Latin os sacrum, translation of Greek hieron osteon ‘sacred bone’ (from the belief that the soul resides in it).