coccyx

n. small triangular bone at the base of the spinal column (Anatomy)

The coccyx (pronounced kok-siks) (Latin: os coccygis), commonly referred to as the tailbone, is the final segment of the human vertebral column, of four fused vertebrae (the coccygeal vertebrae) below the sacrum. It is attached to the sacrum in a fibrocartilaginous joint, which permits limited movement between them. The term coccyx comes originally from the Greek language and means "cuckoo," referring to the shape of a cuckoo's beak.
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Coccyx /coc·cyx/ tail bone; the small bone caudal to the sacrum, formed by union of three to five rudimentary vertebrae, and forming the caudal [more]Coccyx - Community and Resources

Noun
1. the end of the vertebral column in humans and tailless apes
(synonym) tail bone
(hypernym) bone, os
(part-holonym) pelvis, pelvic girdle, pelvic arch, hip
(part-meronym) coccygeal vertebra, caudal vertebra

n. coccyx