noun, plural rachises, rachides [rak-i-deez, rey-ki-] .
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.
Ornithology. the part of the shaft of a feather bearing the web. See illus. under feather.
Anatomy, spinal column.
Also, rhachis.

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

rachidian [ruh-kid-ee-uhn] , rachial [rey-kee-uhl] , rachidial, adjective
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World English Dictionary
rachis or rhachis (ˈreɪkɪs)
n , pl rachises, rhachises, rachides, rhachides
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
3.  another name for spinal column
[C17: via New Latin from Greek rhakhis ridge]
rhachis or rhachis (ˈreɪkɪs, ˈrækɪˌdiːz, ˈreɪ-)
[C17: via New Latin from Greek rhakhis ridge]
rachial or rhachis
rhachial or rhachis
rachidial or rhachis
rhachidial or rhachis

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Medical Dictionary

rachis ra·chis (rā'kĭs)
n. pl. ra·chis·es or rach·i·des (rāk'ĭ-dēz', rā'kĭ-)
See spinal column.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
rachis   (rā'kĭs)  Pronunciation Key 
Plural rachises or rachides (rāk'ĭ-dēz', rā'kĭ-)
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 © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
The rachis has a swollen base, and the entire bipinnately compound leaf is arranged in alternate fashion along the stout twig.
The spikelets are borne on short racemes which branch from the rachis in paniculate fashion.
Spikelet cylindric, placed flatwise at each joint of the rachis and fitting into it.
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