Definition of rachis in English:


(also rhachis)


  • 1Botany
    A stem of a plant, especially a grass, bearing flower stalks at short intervals.

    • ‘Not only does it confer the free-threshing character, but also it influences glume keeledness, rachis toughness, spike length, spike type, and culm height.’
    • ‘Inflorescences are the terminal toothbrush type, with five to 70 pairs of flowers on a rachis approx. 35-50 mm long.’
    • ‘Hordeum spontaneum and H. vulgare are morphologically similar, with the cultivated form having broader leaves, shorter stem and awns, tough ear rachis, a shorter and thicker spike, and larger grains.’
    • ‘This gene did not affect plant height, indicating that the length of rachis and culm are controlled by independent genetic systems.’
    1. 1.1 The midrib of a compound leaf or frond.
      • ‘Leaf width was determined as the sum of the lengths of the two largest leaflets on either side of the rachis.’
      • ‘Because the Sesbania species have pinnately compound leaves, for defoliation the central rachis of the leaf was cut once halfway along its length.’
      • ‘The basal leaves can be more than 10 cm long and have three to eleven leaflets along their rachis.’
      • ‘In fact, leaflets were more elongated and more tightly packed along the leaf rachis in older plants, signifying that the mass was distributed closer to the axis of bending in older plants.’
      • ‘Each leaf has a central rachis to which the many small leaflets are attached.’
  • 2Anatomy
    The vertebral column or the cord from which it develops.

    backbone, spinal column, vertebral column, vertebrae
    View synonyms
  • 3Ornithology
    The shaft of a feather, especially the part bearing the barbs.

    • ‘Feathers (i.e., with well-defined rachis and barbs) are, therefore, most reasonably interpreted as having evolved primarily in association with flight, rather than for thermoregulatory purposes.’
    • ‘A contour feather, as a typical feather, has a complex morphology consisting of a central shaft or rachis to which barbs are attached on two margins to form a vane.’
    • ‘Feathers, however bizarre or morphologically complex, consist essentially of a rachis, barbs, and barbules.’
    • ‘Natal downs frequently lack a rachis, but numerous barbs come together at a common point.’
    • ‘Beipiaosaurus and Sinomithosaurus bear short fibers similar to those on Sinosauropteryx, but the structures on Caudipteryx and Protarchaeopteryx are unambiguous feathers, with a central rachis and barbs.’


Late 18th century: modern Latin, from Greek rhakhis ‘spine’. The English plural -ides is by false analogy.