Rachis

//ˈɹeɪkɪs// noun

noun ·Uncommon ·Advanced level

Definitions

Noun
  1. 1
    The spinal column, or the vertebrae of the spine. obsolete
  2. 2
    the series of vertebrae forming the axis of the skeleton and protecting the spinal cord wordnet
  3. 3
    An anatomical shaft or axis in a marine invertebrate.

    "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."

  4. 4
    axis of a compound leaf or compound inflorescence wordnet
  5. 5
    The central shaft of a feather.
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  1. 6
    The axis of either a compound leaf, inflorescence, or fern frond.

Synonyms

All synonyms
backbackbonebonemiddle ribmidribshaft

Example

More examples

"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."

Etymology

From New Latin rachis, from Ancient Greek ῥάχις (rhákhis, “spine, ridge”).

Related phrases

spinal column

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Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.