| Noun | 1. | tail bone - the end of the vertebral column in humans and tailless apesspinal column, spine, vertebral column, rachis, backbone, back - the series of vertebrae forming the axis of the skeleton and protecting the spinal cord; "the fall broke his back" caudal vertebra, coccygeal vertebra - one of 4 vertebrae in the human coccyx pelvic arch, pelvic girdle, pelvis, hip - the structure of the vertebrate skeleton supporting the lower limbs in humans and the hind limbs or corresponding parts in other vertebrates |