Another spelling bee word I never saw before, but should have.
rachis
n.,
pl. ra4chis ModL < Gr rhachis, backbone < IE base *wraDh3, thorn, point > Lith rQxas, stubble6
1 SPINAL COLUMN
2 Bot. the principal axis of an inflorescence or of a compound leaf
3 Zool. the shaft of a feather, esp. that part bearing the barbs: see FEATHER, illus.

But we should all know "rickets" the skeletal disease resulting from lack of Vitamin D.