from
The Collaborative International Dictionary of English v.0.48
Rhachis \Rha"chis\, n.; pl. E. {Rhachises}, L. {Rhachides}. [See
{Rachis}.] [Written also {rechis}.]
1. (Anat.) The spine.
[1913 Webster]
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.
[1913 Webster]
3. (Zool.)
(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.
[1913 Webster]