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- (obsolete, zoology, anatomy) The spinal column, or the vertebrae of the spine. [17th-19th c.]
- (zoology) An anatomical shaft or axis in a marine invertebrate. [from 18th c.]
- 2017, Danna Staaf, Squid Empire, ForeEdge, →ISBN, page 115:
- In some squid species, the pen rachis flares out into wings on either side, and the tip of the rachis grows into a thick cone.
- (ornithology) The central shaft of a feather. [from 19th c.]
- (botany) The main shaft of either a compound leaf, head of grain, or fern frond. [from 19th c.]
- The plural form rachides is based on a mistaken impression of the Ancient Greek stem.
main shaft of a compound leaf or head of grain
central shaft of a feather
- rachis at OneLook Dictionary Search
- rachis in The Century Dictionary, The Century Co., New York, 1911