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.

I've seen rachis before in passages about birds--in bird books! Surprisingly, I did not realize the term also applied to the central stem of the compound leaf, and I've done by far more reading in tree books than in bird books. So, wow! Cool to know what the central stem of the compound leaf is called.

Many times I 've considered the similarity between birds and trees--here's just another instance.

It's interesting that such a soft creature has such hard parts--rachis, rictus, bones (naturally), and even the grit eaten for those that have gizzards.

Edit: Do all birds have gizzards? Even hummingbirds?