Definition of rachis in English:

rachis

(also rhachis)

Pronunciation /ˈrākis/ /ˈreɪkɪs/

nounrachides

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

    ‘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.’
    • ‘Not only does it confer the free-threshing character, but also it influences glume keeledness, rachis toughness, spike length, spike type, and culm height.’
    1. 1.1The midrib of a compound leaf or frond.
      ‘Because the Sesbania species have pinnately compound leaves, for defoliation the central rachis of the leaf was cut once halfway along its length.’
      • ‘Each leaf has a central rachis to which the many small leaflets are attached.’
      • ‘The basal leaves can be more than 10 cm long and have three to eleven leaflets along their rachis.’
      • ‘Leaf width was determined as the sum of the lengths of the two largest leaflets on either side of the 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.’
  • 2Anatomy
    The vertebral column or the cord from which it develops.

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

    ‘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.’
    • ‘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.’
    • ‘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.’
    • ‘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.’
    quill

Origin

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