coccyx: [17] The Greek physician Galen considered that the small tapering bone at the base of the human spine resembled a cuckoo’s beak. He therefore named it kókkux, which was Greek for ‘cuckoo’. It reached English via the Latin form coccyx.
1610s, from Latin coccyx, from Greek kokkyx "cuckoo" (from kokku, like the bird's English name echoic of its cry), so called by ancient Greek physician Galen because the bone in humans supposedly resembles a cuckoo's beak.
