\Rha"chis\, n.; pl. E. {Rhachises}, L. {Rhachides}. [See
{Rachis}.] [Written also {rechis}.]
1. (Anat.) The spine.
2. (Bot.)
   (a) The continued stem or midrib of a pinnately compound
       leaf, as in a rose leaf or a fern.
   (b) The principal axis in a raceme, spike, panicle, or
       corymb.
3. (Zo["o]l.)
   (a) The shaft of a feather. The rhachis of the
       after-shaft, or plumule, is called the hyporhachis.
   (b) The central cord in the stem of a crinoid.
   (c) The median part of the radula of a mollusk.
   (d) A central cord of the ovary of nematodes.