Azygos - azygos, unyoked (not a pair) named for its asymmetry.⏎
Cauda equina - cauda equina, horse's tail.⏎
Arachnoid - arachne, spider; like a spider's web⏎
Appendix - ad, toward; pendere, to hang. Hence appendage.⏎
Cruciate - crux (crucis), a cross.⏎