Rhachis
Pronunciation : Rha"chis, n.; pl. E. Rhachises
Part of Speech : L.
Etymology : [See Rachis.] [Written also rechis.]
Definition : 1. (Anat.)
Defn: 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?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.
Rhachides.
Source : Webster's Unabridged Dictionary, 1913