1. A concave surface or curve.
  2. The vault of the sky.
  3. One of the celestial spheres of the Ptolemaic or geocentric model of the world.
    Aristotle makes 1 to move to the concave of the Moon. - Thomas Salusbury (1661).
  4. An element of a curved grid used to separate desirable material from tailings or chaff in mining and harvesting.
  5. An indentation running along the base of a surfboard, intended to increase lift.
  6. An indented area on the top of a skateboard, providing a position for foot placement and increasing board strength.


  1. To render concave, or increase the degree of concavity.


  1. curved like the inner surface of a sphere or bowl
  2. not convex; arranged such that there exist at least two points for which a straight line between these points does not lie wholly within the set.
  3. having an epigraph which is a concave set.
  4. hollow; empty

The above text is a snippet from Wiktionary: concave
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