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.
coccyx coc·cyx (kŏk'sĭks)
n. pl. coc·cy·ges (kŏk-sī'jēz, kŏk'sĭ-jēz')
The small triangular bone located at the base of the spinal column, formed by the fusion of four rudimentary vertebrae, and articulating above with the sacrum. Also called tailbone.