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- curved like the inner surface of a sphere or bowl
- (set theory, not comparable, of a set) 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.
- (functional analysis, not comparable, of a real-valued function on the reals) having an epigraph which is a concave set.
- hollow; empty
- as concave […] as a worm-eaten nut
concave (plural concaves)
- A concave surface or curve.
- The vault of the sky.
- One of the celestial spheres of the Ptolemaic or geocentric model of the world.
- Aristotle makes [Fire] to move to the concave of the Moon. - Thomas Salusbury (1661).
- (manufacturing) An element of a curved grid used to separate desirable material from tailings or chaff in mining and harvesting.
- (surfing) An indentation running along the base of a surfboard, intended to increase lift.
- (skateboarding) An indented area on the top of a skateboard, providing a position for foot placement and increasing board strength.
A concave surface or curve
To render concave, or increase the degree of concavity.