Definitions

1. adjective

Relating to or situated near the spine, especially the coccyx or tailbone.

“The rachidian vertebrae are the final set of bones in the spinal column.”

2. noun

Either of the last two pairs of abdominal segments of an insect, which are fused to form the tergum and sternum, and in the male often modified to form the genital organs.

“In the insect anatomy, the rachidian segments play a crucial role in the reproductive system.”