Entry: coccyx (n.)
In context: "Her posture, that night, with her coccyx against something and looking down the length of her legs, was awfully close to the way Himself used to stand around."
Definition: The small triangular bone appended to the point of the sacrum and forming the termination of the spinal column in humans, formed by the coalescence of four rudimental coccygeal vertebræ; also, an analogous part in birds or other animals.
Other: I prefer to call it the 'rumpbone':
1615 H. Crooke Μικροκοσμογραϕια 493 In Dogs and Apes there are three coniugations proceeding out of the Coccyx or rump-bone.
SNOOT score: 1
Source: Oxford English Dictionary