A large triangular bone at the base of the spine, located between the two ilia (wings of the pelvis) and formed from vertebrae that fuse in adulthood.
Origin
From Latin os sacer, a [[calque of Ancient Greek [[ἱερός. Apparently so called either because the sacrum was the part of the animal offered in sacrifice or because of a putative belief that it is where a person's soul resides. A third explanation is that the term is a mistranslation of Ancient Greek ἱερός, which has two meanings: “holy, sacred”, and “big” — big being a more appropriate description of the sacrum — but compare.
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