Entry 1 sense Webster, 1913 Rachidian /(rȧ*kĭd"ĭ*an)/ · Ra·chid·i·an · IPA 01 a. Of or pertaining to the rachis; spinal; vertebral. Same as Rhachidian. 1. Of or pertaining to the rachis; spinal; vertebral. Same as Rhachidian.(Anat. & Zool.) See: Rhachidian