Definify.com
Webster 1913 Edition
Rhachis
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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.
(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.