coccyx

noun

Etymology: From Latin coccyx, from Ancient Greek κόκκυξ (kókkux, “cuckoo”), referring to the curved shape of a cuckoo's beak when viewed from the side.

1. The final (bottom-most) fused vertebrae at the base of the spine, the tailbone.

   “He lands on the concrete path and bounces on his coccyx, which cracks the base of his spine.”

   “An actor herself, McAlpine was hands-on, demonstrating “how you penetrate” on screen: “If you can move your coccyx, just arch your back slightly, it looks fantastic,” she says happily. “Those orgy scenes were amazing.””