sacrum

Word History: The human sacrum consists of five fused vertebrae, to which the coccyx or tailbone—the vestigial remnant of a tail—is attached. In Latin, this large bone was called os sacrum, literally "holy bone." (Os means "bone" in Latin, and sacrum is a form of the Latin adjective sacer, "holy," which is also the source of a number of other English words like sacred, sacrifice, and sacrilege.) The Latin term for the bone is in turn a translation of its Greek name, hieron osteon. (Hieron is a form of the Greek adjective hieros, "holy," while osteon means "bone" in Greek.) In ancient Greek animal sacrifices, certain portions of the victim were reserved for the gods, and among these was the sacrum with the tail still attached. After the gods' portions were placed in the sacrificial fire, a seer or diviner would often observe how the tail curled and sputtered in the flames, and he would interpret these signs as favorable or unfavorable. Greek representations of animal sacrifices on painted ceramics often show the tail curling in the fire and thus revealing the will of the gods.