(obsolete, zoology, anatomy) The spinal column, or the vertebrae of the spine. / (zoology) An anatomical shaft or axis in a marine invertebrate. / (ornithology) The central shaft of a feather.

(medicine, anatomy) Of or pertaining to the back.

plural of rachis

A developmental birth defect in which the neural tube fails to close completely, leading to motor and sensory deficits, chronic infections, and disturbances in bladder function.