Curved like the inner surface of a sphere or bowl.
Hollow; empty.
Satisfying the property that all segments connecting two points on the function's graph lie below the function.
Not convex; having at least one internal angle greater than 180 degrees.
A playing card made concave for use in cheating.
One of the celestial spheres of the Ptolemaic or geocentric model of the world.
An indentation running along the base of a surfboard, intended to increase lift.
An element of a curved grid used to separate desirable material from tailings or chaff in mining and harvesting.
The vault of the sky.
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.
Situated on the inside; that is within, inner; belonging to the inside.
Not superficially obvious, inner, not expressed, especially relating to mental or spiritual faculties as opposed to external ones.
Moving or tending toward the inside.
Towards the inside.
Towards one’s mind, thoughts, or internal self.