Definition of costa in US English:


nounPlural costae

Zoology Botany
  • 1A rib, midrib, or riblike structure.

    • ‘Wall thickness is 10-26 m, becoming thicker at the corners of the chamber where it may bulge outwardly to produce coarse longitudinal costae.’
    • ‘The main part of the shell is coarsely commarginally lamellose and lacks radial costae.’
    • ‘It has strong divaricate ornamentation of coarse costae and/or small plicae, which bear low, close nodes, but which cover both the anterior and posterior faces of the shell.’
    • ‘He differentiated his new species from S. robusta by its more numerous costae on the shell flanks.’
    • ‘The internal molds are smooth with exception of traces of the concentric costae on the rostral face.’
    1. 1.1Entomology The main vein running along the leading edge of an insect's wing.
      • ‘The forewings generally are reduced to the region immediately adjacent to the costa, having separated along the radius and cubitus veins.’
      • ‘It resulted in outgrowths and duplications of the costa region of the wing.’


Mid 19th century: from Latin.