Coccyx, the tail bone, comes from kokkyx, Greek for cuckoo. One of the oldest words in anatomy, it was coined around 300 B.C. by Herophilus who, it is said, was inspired by the cuckoo's bill (probably that of the common cuckoo, Cuculus canorus). However, he was more likely taken by the anterior portion of the cuccko skull, which bears a greater resemblance to the coccyx than just the bill alone (see the photos below).

A more fanciful explanation of the link between cuckoo and coccyx was provided in the early 17th century by the French anatomist and surgeon Johann Riolan, who inexplicably insisted that the sound of flatus emanating from the coccygeal region was reminiscent of the call of a cuckoo and thus was the inspiration for Herophilus. Never mind that neither the male nor the female of any cuckoo species has a call that you'd confuse with flatulence (indeed, the classic sound of the cuckoo clock was patterned after the call of the male common cuckoo). Perhaps the professeur simply had a talented friend.

Nonetheless, the coccyx has been called the "whistle bone" for its proximity to the source of digestive tract toots.

Unrelated but interesting: The word "cuckold" (a man whose wife has cheated on him) also comes from cuckoo, derived from the female's nasty habit of laying eggs in nests not her own and thus tricking other birds into raising her young. Likewise, a cuckold may raise children that aren't his.

Image credits

coccyx from

summit.stanford.edu
The common cuckoo from

www.xpress.se/~jani0084/2005.htm
cuckoo skull
www.skullsite.com