| rachet | (noun) mechanical device consisting of a toothed wheel or rack engaged with a pawl that permits it to move in only one direction | Synonyms: ratch, ratchet |
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| rachis | (noun) the series of vertebrae forming the axis of the skeleton and protecting the spinal cord | Synonyms: back, backbone, spinal column, spine, vertebral column |
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| (noun) axis of a compound leaf or compound inflorescence | - |
| rachischisis | (noun) a not uncommon congenital defect in which a vertebra is malformed; unless several vertebrae are affected or there is myelomeningocele there are few symptoms; can be diagnosed by amniocentesis | Synonyms: schistorrhachis, spina bifida |
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| rachitis | (noun) childhood disease caused by deficiency of vitamin D and sunlight associated with impaired metabolism of calcium and phosphorus | Synonyms: rickets |
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| (noun) inflammation of the vertebral column | - |