sacrum Look up sacrum at Dictionary.com
"bone at the base of the spine," 1753, from L.L. os sacrum "sacred bone," from L. os "bone" + sacrum, neut. of sacer "sacred." Said to be so called because the bone was the part of animals that was offered in sacrifices. Translation of Gk. hieron osteon. But Gk. hieros also can mean "strong."