or rha·chis

[ rey-kis ]
See synonyms for rachis on Thesaurus.com
noun,plural ra·chis·es, rach·i·des [rak-i-deez, rey-ki-]. /ˈræk ɪˌdiz, ˈreɪ kɪ-/.
  1. Botany.

    • the axis of an inflorescence when somewhat elongated, as in a raceme.

    • (in a pinnately compound leaf or frond) the prolongation of the petiole along which the leaflets are disposed.

    • any of various axial structures.

  2. Ornithology. the part of the shaft of a feather bearing the web.

  1. Anatomy. spinal column.

Origin of rachis

1775–85; <New Latin <Greek rháchis spine, ridge, backbone

Other words from rachis

  • ra·chid·i·an [ruh-kid-ee-uhn], /rəˈkɪd i ən/, ra·chi·al [rey-kee-uhl], /ˈreɪ ki əl/, ra·chid·i·al, adjective

Words Nearby rachis

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use rachis in a sentence

  • The pinnules are from a line to two lines long, and are adnate to the secondary rachis by a more or less decurrent base.

    Beautiful Ferns | Daniel Cady Eaton
  • The stipes is somewhat longer than the rachis, and it is of a whity-green colour.

    How to Know the Ferns | S. Leonard Bastin
  • A simple inflorescence of flowers on pedicels of equal length arranged on a common, elongated axis (rachis).

    Michigan Trees | Charles Herbert Otis
  • A simple inflorescence of sessile flowers arranged on a common, elongated axis (rachis).

    Michigan Trees | Charles Herbert Otis
  • Under these conditions the midvein is called the rachis (a), and the divisions are called the pinn (b).

    How to Know the Ferns | Frances Theodora Parsons

British Dictionary definitions for rachis



/ (ˈreɪkɪs) /

nounplural rachises, rhachises, rachides or rhachides (ˈrækɪˌdiːz, ˈreɪ-)
  1. botany the main axis or stem of an inflorescence or compound leaf

  2. ornithol the shaft of a feather, esp the part that carries the barbs

  1. another name for spinal column

Origin of rachis

C17: via New Latin from Greek rhakhis ridge

Derived forms of rachis

  • rachial or rhachial (ˈreɪkɪəl) or rachidial or rhachidial (rəˈkɪdɪəl), adjective

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for rachis


[ kĭs ]

Plural rachises rachides (răkĭ-dēz′, rākĭ-)
  1. A main axis or shaft, such as the main stem of an inflorescence, the stalk of a pinnately compound leaf, the shaft of a feather, or the spinal column.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.