The Collaborative International Dictionary of English v.0.48:

Rachis \Ra"chis\ (r[=a]"k[i^]s), n.; pl. E. Rachises
   (r[=a]"k[i^]s*[e^]z), L. Rachides (r[a^]k"[i^]*d[=e]z).
   [NL., fr. Gr. "ra`chis, -ios.] [Written also rhachis.]
   1. (Anat.) The spine; the vertebral column.
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   2. (Bot. & Zool.) Same as Rhachis.
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